Resolve "Add a UI configuration option to the group settings like Allow personal snippets"

What does this MR do and why?

Problem

We want to allow users to modify Allow personal snippets settings using UI.

The value of this setting is stored in database (see Add allow_personal_snippets field to group sett... (#555051 - closed)).

Proposal

• Update UI to allow users to enable/disable this configuration.
• Document the new configuration option
• This functionality should be released behind the feature flag.

Additional Notes

The ability to toggle this setting should only be available to group owners and should only impact enterprise users in the namespace.

API counterpart issue: Allow to display and update allow_personal_snip... (#555053)

Similar implementation

Disable personal access tokens for enterprise u... (!148415 - merged)

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Go to qa/gdk/gdk.yml

   env:
     GITLAB_SIMULATE_SAAS: 1

2. restart gdk

3. In rails console enable the feature flag

    Feature.enable(:allow_personal_snippets_setting)

4. Check permission http://localhost:3000/groups/toolbox/-/edit#js-permissions-settings for the checkbox Allow personal snippet

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #552392 (closed)