Resolve "Bug with visibility levels in snippets when VUE is enabled"

What does this MR do?

The MR connects snippet's "Visibility level" radio buttons with admin settings in /admin/application_settings/general#js-visibility-settings to reflect all possible restrictions that can be driven from the admin settings.

NB: since the whole Vue refactoring of the snippet edit form is still behind a feature flag, the changelog entry has not been provided.

How to click-test

1. Enable :snippets_edit_vue feature flag in Rails console
2. Logged in as admin, go to /admin/application_settings/general#js-visibility-settings and play with the following settings:
   • Restricted visibility levels, and
   • Default snippet visibility
3. Open another browser or an Incognito tag of the current browser and log in as a regular user (not admin)
4. Go to /-/snippets/new and make sure the "Visibility level" field (right below the blob) follow the settings set on step 2

Screenshots

Settings	Before	After
🍏 No restrictions. Default visibility is respected
🍊 All except just one levels are restricted
🍊 Default visibility restricted
🔴 All visibilities restricted

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

References #241468 (closed)