Split Feature Flags visibility setting from Operations

What does this MR do and why?

This MR contains backend changes for separating the visibility setting of Feature Flags from the Operations setting it is currently controlled by.

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(feature_flags_access_level: 'enabled')

MR acceptance checklist

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