Add caption support with new models, vuex, and edit modal integration

[akash5100]

Summary

Description of the change(s) you made

This PR adds caption files and cues models leveraging the change event architecture. It also:

Frontend

• Adds a new Captions tab to the edit modal for managing and generating captions, visually controlled by feature flags
• A new "caption" directory has been added under channelEdit vuex to manage the state for captions. Which is integrated into the EditModal and EditList components.

Backend

• Adds support for captions by introducing new CaptionFile and CaptionCue models. The models leverage the change event architecture to track changes.
• Tests have been added for the DRF endpoint to ensure it works properly with the sync API architecture.

Manual verification steps

TODO

References

Comments

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Contributor's Checklist

PR process:

• If this is an important user-facing change, PR or related issue the CHANGELOG label been added to this PR. Note: items with this label will be added to the CHANGELOG at a later time
• If this includes an internal dependency change, a link to the diff is provided
• The docs label has been added if this introduces a change that needs to be updated in the user docs?
• If any Python requirements have changed, the updated requirements.txt files also included in this PR
• Opportunities for using Google Analytics here are noted
• Migrations are safe for a large db

Studio-specifc:

• All user-facing strings are translated properly
• The notranslate class been added to elements that shouldn't be translated by Google Chrome's automatic translation feature (e.g. icons, user-generated text)
• All UI components are LTR and RTL compliant
• Views are organized into pages, components, and layouts directories as described in the docs
• Users' storage used is recalculated properly on any changes to main tree files
• If there new ways this uses user data that needs to be factored into our Privacy Policy, it has been noted.

Testing:

• Code is clean and well-commented
• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Any new interactions have been added to the QA Sheet
• Critical and brittle code paths are covered by unit tests

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Reviewer's Checklist

This section is for reviewers to fill out.

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[bjester]

Similarly to the above comment, could you also check File.filter_edit_queryset here

[akash5100]

        if file_id:
            allowed_file_id = set(
                File.filter_edit_queryset(
                    File.objects.get(pk=file_id), self.request.user
                )
                .values_list("id", flat=True)
            )
            queryset = queryset.filter(file_id=allowed_file_id)

Please check this.

I think there won't be comma seperated file_ids. (we don't actually use this query for now)