Add feature toggle for Releases (backend)

What does this MR do and why?

This MR contains backend changes for creating a project-level feature toggle for Releases.

This change is behind the split_operations_visibility_permissions FF (introduced in !89089 (diffs)), which is disabled by default.

Related to #361586 (closed)

Screenshots or screen recordings

Setting	FF OFF	FF ON
OFF
ON

How to set up and validate locally

Enable FF:

Feature.enable(:split_operations_visibility_permissions, project)

Enable setting:

project.update(releases_access_level: 'enabled')

MR acceptance checklist

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