[WIP] [Draft] Bump PHP to 8.1 & Symfony to 5.4 plus dependencies

[jefferya]

In-progress.

The problem: update to PHP 8 and Symfony 5.4 LTS versions (plus dependancies) and remove deprecation messages

• Update to PHP 8.1, Symphony 5.4 (LTS version) and dependencies
• Fixes:
  • Symfony v4 deprecation: "Symfony\Bundle\FrameworkBundle\Command\ContainerAwareCommand
  • Command::execute() should always return int in Symfony 5+
  • Twig v2.7 deprecations

What has been tested

• create_bag with default plugins (bag exists 2023-01-19; I lacked the time to fully verify each file constituting the bag)
• get_queue
• process_queue
• REST interface (api/createbag): via the Isle-Buildkit PHP 8.1 nginx container
• crontab entry to consume the queue
• register_bags_with_islandora: true (requires https://github.com/mjordan/islandora_bagger_integration/pull/31)

The testing infrastructure is defined: in https://github.com/cwrc/isle-bagger which builds upon an Isle Buildkit PHP 8.1 container (unreleased as of 2023-01-19) -- see the aforementioned link for details.

Todo:

• check if this is still relevant: https://github.com/mjordan/islandora_bagger/issues/78