feat: Enable overriding widget classes

[HT-Moh]

• Move widget class variables to settings for centralized management.
• Update widgets to retrieve class attributes using the get_config function.
• Include new variables in the get_config function to support customization.
• Clean up imports in admin files and use get_config for widget classes.
• Using get_config on forms.py and sites.py
• Using get_config on filters and import_export forms.py

Usage: settings.py

BASE_CLASSES = [
  'border',
  'bg-white',
  'font-medium',
  'rounded-md',
  'shadow-sm',
  'text-gray-500',
  'text-sm',
  'focus:ring',
  'focus:ring-primary-300',
  'focus:border-primary-600',
  'focus:outline-none',
  'group-[.errors]:border-red-600',
  'group-[.errors]:focus:ring-red-200',
  'dark:bg-gray-900',
  'dark:border-gray-700',
  'dark:text-gray-400',
  'dark:focus:border-primary-600',
  'dark:focus:ring-primary-700',
  'dark:focus:ring-opacity-50',
  'dark:group-[.errors]:border-red-500',
  'dark:group-[.errors]:focus:ring-red-600/40',
]

SELECT_CLASSES = [
  *BASE_CLASSES,
  'px-3',
  'py-2',
  'pr-8',
  'flex-grow',
  'max-w-2xl',
  'appearance-none',
  'truncate',
]

UNFOLD = {
  'SITE_TITLE': "Site name",
  'SITE_HEADER': None
  'SELECT_CLASSES': SELECT_CLASSES,
}

You can change classed by adding them to UNFOLD

340

[lukasvinclav]

@HT-Moh this is actually what I'm already considering to implement and below you can see one of the first steps making CSS classes available in all templates where it would be possible to change them in settings.py. But this change will require much more work. All form elements have to use these classes what is not the case right now (some inputs have hardcoded CSS in templates) so a lot of refactoring and UI redesign will be required.

https://github.com/unfoldadmin/django-unfold/blob/main/src/unfold/sites.py#L56

At the moment, I'm recommending you to change the visual of inputs by loading of your custom CSS file

[HT-Moh]

@lukasvinclav thanks, yeah but this PR made it possible now to change it on the settings. 10 files has been refactored and the necessary changes on the sites.py is already done.