[Testing] Enable cover block uploads behind dev flag

[mkevins]

Description

This PR is the first step toward resolving wordpress-mobile/gutenberg-mobile#1739. This PR enables upload options for the Cover block behind the __DEV__ flag, and adds a progress bar to ongoing uploads. More details can be found within the individual gutenberg PRs.

Related PRs:

• gutenberg
  • Enable uploads dev only: [Mobile] Enable cover block uploads - dev only WordPress/gutenberg#21196
  • Upload progress: [Mobile] Cover block upload progress WordPress/gutenberg#21197
• gutenberg-mobile: Enable cover block uploads behind dev flag gutenberg-mobile#2070
• WordPress-Android: Cover block upload completion processor WordPress-Android#11541

To test:

Testing steps are provided in the related gutenberg PRs.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

	Warnings
⚠️	This PR is tagged with 'DO NOT MERGE'.
⚠️	PR is not assigned to a milestone.

Generated by 🚫 dangerJS

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading it from AppCenter here with build number: 26584. IPA is available here. If you need access to this, you can ask a maintainer to add you.

[github-actions]

	Warnings
⚠️	This PR is tagged with 'DO NOT MERGE'.

Generated by 🚫 dangerJS against 4c3f91a

[SergioEstevao]

@mkevins do we need to implement a background upload processor specific for this block?

[mkevins]

For posterity: processors are implemented here: #13928