Implement revisions tab (Step 4)(Iteration N)

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Important: All the new functionality must be implemented behind the feature flag :version_snippets. Besides, it has to be scoped for projects. Therefore, instead of checking if the feature flag is enabled or not (Feature.enabled?(:version_snippets)), we will check if the feature flag is enabled for specific users (Feature.enabled?(:version_snippets, user)).

UX Proposal

Add a Revisions tab

• Display a list of revisions when the user clicks the Revisions tab
• For each revisions display:
  • Avatar of the user that made the revision
  • Name of the user that made the revision
  • When the revision was made
  • Count of files, added lines, removed lines
  • The associated diffs
  • Diffs are displayed expanded by default but should be collapsable
• Load the 5 most recent revisions
• If more than 5 revisions exist, show pagination controls to load additional

Description	Mockup
Revisions tab

Availability and Testing

Potentially requires E2E coverage

Security Testing

• Ensure visibility of revisions (@lulalala )

Testing Activity

• Test to check that we display the information we need (@fjsanpedro)

QA Testing

This change warrants a new end-to-end test, new issue for it to be created and linked (@a_mcdonald).

NB Please include the SET (@a_mcdonald) in your MR reviews to coordinate the progress.