Translation submit/update form components

[zerolab]

This PR provides a mechanism to add new form components to the submit/update translations views.

It takes the existing mechanism used on the locale edit forms

When submitting a translation we can get one or more translation sources with at least one corresponding translation sources. This should be accounted for by hte new TranslationComponentManager.

New component registration can be done using the new register_translation_component decorator

@register_translation_component(
    heading=gettext_lazy("My component"),
    help_text=gettext_lazy("Help text to describe what this is needed for"),
    enable_text=gettext_lazy("Add custom component data"),
    disable_text=gettext_lazy("Do not add custom component data"),
)
class MyTranslationComponent(model.Model):
    pass

Did not yet add documentation as register_locale_component is not documented. Let's discuss

[codecov-commenter]

Codecov Report

Merging #491 (d25aefb) into main (f6f6b00) will decrease coverage by 0.20%.
The diff coverage is 88.75%.

@@            Coverage Diff             @@
##             main     #491      +/-   ##
==========================================
- Coverage   93.02%   92.82%   -0.21%     
==========================================
  Files          35       36       +1     
  Lines        2868     2981     +113     
  Branches      449      467      +18     
==========================================
+ Hits         2668     2767      +99     
- Misses        104      114      +10     
- Partials       96      100       +4     

Impacted Files	Coverage Δ
wagtail_localize/views/update_translations.py	92.95% <72.22%> (+0.53%)	⬆️
wagtail_localize/components.py	85.56% <85.56%> (ø)
wagtail_localize/locales/views.py	97.22% <100.00%> (-0.20%)	⬇️
wagtail_localize/test/models.py	97.39% <100.00%> (+0.18%)	⬆️
wagtail_localize/views/submit_translations.py	93.83% <100.00%> (+0.40%)	⬆️

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[kaedroho]

This all looks good to me, nice work!