Add a toggle to enable or disable feature flags

What does this MR do and why?

As part of splitting out the operations toggle, the feature flags need their own toggle.

Note that the operations toggle will remain until the split is complete.

Also no changelog entry as this is still behind a feature flag.

Screenshots or screen recordings

How to set up and validate locally

Enable the toggle

Feature.enable(:split_operations_visibility_permissions)

1. Visit any project's settings
2. Expand the visibility section

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

for #361586 (closed)