Closes #875 Add new option to select next-gen format

[remyperona]

Description

Add a new UI setting option to select the next-gen format to generate, or disable it.

Fixes #875

• [x] Enhancement (non-breaking change which improves an existing functionality).

Checklists

Feature validation

• [ ] I validated all the Acceptance Criteria. If possible, provide sreenshots or videos.
• [ ] I triggered all changed lines of code at least once without new errors/warnings/notices.

Code style

• [ ] I wrote self-explanatory code about what it does.
• [ ] I wrote comments to explain why it does it.
• [ ] I named variables and functions explicitely.
• [ ] I protected entry points against unexpected inputs.
• [ ] I did not introduce unecessary complexity.

Observability

• [ ] I handled errors when needed.
• [ ] I wrote user-facing messages that are understandable and provide actionable feedbacks.
• [ ] I prepared ways to observe the implemented system (logs, data, etc.).

[Mai-Saad]

@Tabrisrp Thanks for the PR, please find exploratory test notes below (WIP)

• Next-gen options shall match that on Epic i.e NONE then WEBP then AVIF => seems Notion wasn't updated and ok as is

• [x] Warning after uploading images with a fresh install of Imagify and optimization, it keeps loading 1- fresh install and activate of Imagify 2- upload image => see the warning

• [x] Fatal error when uploading image/ optimize image while filter is used 1- fresh install/activation of Imagify 2- Enable the Next-Gen filter

  add_filter('imagify_nextgen_images_formats', function($formats){
  $formats['webp'] = 'webp';
  
  return $formats ;
  });

  3- upload an image or click optimize for a previously uploaded image

[18-Apr-2024 07:27:09 UTC] PHP Fatal error:  Uncaught TypeError: Imagify\Optimization\Process\AbstractProcess::get_suffix_from_format(): Argument #1 ($format) must be of type string, null given, called in /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/classes/Optimization/Process/AbstractProcess.php on line 1554 and defined in /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/classes/Optimization/Process/AbstractProcess.php:1570
Stack trace:
#0 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/classes/Optimization/Process/AbstractProcess.php(1554): Imagify\Optimization\Process\AbstractProcess->get_suffix_from_format()
#1 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/classes/Optimization/Process/AbstractProcess.php(500): Imagify\Optimization\Process\AbstractProcess->is_size_next_gen()
#2 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/classes/Job/MediaOptimization.php(181): Imagify\Optimization\Process\AbstractProcess->optimize_size()
#3 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/classes/Job/MediaOptimization.php(66): Imagify\Job\MediaOptimization->task_optimize()
#4 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/inc/classes/Dependencies/deliciousbrains/wp-background-processing/classes/wp-background-process.php(516): Imagify\Job\MediaOptimization->task()
#5 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/inc/classes/Dependencies/deliciousbrains/wp-background-processing/classes/wp-background-process.php(333): Imagify_WP_Background_Process->handle()
#6 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/class-wp-hook.php(324): Imagify_WP_Background_Process->maybe_handle()
#7 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#8 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/plugin.php(517): WP_Hook->do_action()
#9 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-admin/admin-ajax.php(192): do_action()
#10 {main}
  thrown in /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify-plugin/classes/Optimization/Process/AbstractProcess.php on line 1570

• [ ] Grey out the options while the filter is enabled needs improvement (lighter in color, Read me is a link) => details here https://wp-media.slack.com/archives/CUKB44GNN/p1713425370986549?thread_ts=1713374092.801659&cid=CUKB44GNN
• [x] Error after update from 2.2.1 while avif is enabled 1- install and activate 2.2.1 2- Enable avif 3- upload a couple of images => next-gen is added 4- update to 2.2.2 and open Imagify settings

  [18-Apr-2024 08:20:03 UTC] PHP Deprecated:  strpos(): Passing null to parameter #2 ($needle) of type string is deprecated in /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/classes/Bulk/WP.php on line 194
  [18-Apr-2024 08:20:03 UTC] PHP Deprecated:  strtoupper(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/classes/Bulk/WP.php on line 208
  [18-Apr-2024 08:20:03 UTC] PHP Fatal error:  Uncaught Error: Undefined constant Imagify\Optimization\Process\WP::_SUFFIX in /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/classes/Bulk/WP.php:208
  Stack trace:
  #0 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/classes/Bulk/WP.php(208): constant()
  #1 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/classes/Bulk/Bulk.php(237): Imagify\Bulk\WP->get_optimized_media_ids_without_format()
  #2 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/classes/Bulk/Bulk.php(606): Imagify\Bulk\Bulk->run_generate_nextgen()
  #3 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/class-wp-hook.php(326): Imagify\Bulk\Bulk->maybe_generate_missing_nextgen()
  #4 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
  #5 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/plugin.php(517): WP_Hook->do_action()
  #6 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/option.php(889): do_action()
  #7 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/inc/classes/class-imagify-abstract-options.php(372): update_option()
  #8 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/inc/classes/class-imagify-abstract-options.php(231): Imagify_Abstract_Options->set_raw()
  #9 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/inc/admin/upgrader.php(318): Imagify_Abstract_Options->set()
  #10 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/class-wp-hook.php(324): _imagify_new_upgrade()
  #11 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
  #12 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/plugin.php(517): WP_Hook->do_action()
  #13 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/inc/admin/upgrader.php(69): do_action()
  #14 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/class-wp-hook.php(324): _imagify_upgrader()
  #15 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
  #16 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-includes/plugin.php(517): WP_Hook->do_action()
  #17 /var/www/mai.rocketlabsqa.ovh/htdocs/wp-admin/admin-ajax.php(45): do_action()
  #18 {main}
  thrown in /var/www/mai.rocketlabsqa.ovh/htdocs/wp-content/plugins/imagify/classes/Bulk/WP.php on line 208

  Note: the same fatal error occurred if we enabled avif and save settings after a fresh install of 2.2.2