Show Disabled "Add Approval Rule" Button with Explanatory Tooltip

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Problem Statement

A large Ultimate, Self-Managed customer ran into the situation where the instance-level setting "Prevent editing approval rules in projects and merge requests" was enabled, and the "Add approval rule" button completely disappears from Project Settings → Merge requests without any explanation. This creates a poor user experience where Maintainers expect to be able to configure approval rules but cannot find the functionality.

Current Behavior

• User navigates to Project Settings → Merge requests → Merge request approvals section
• "Add approval rule" button is completely missing from the "Approval rules" section
• No indication of why it's unavailable

Proposed Behavior

When the admin setting "Prevent editing approval rules in projects and merge requests" is enabled, instead of hiding the "Add approval rule" button completely, GitLab should behave the following way:

1. User navigates to Project Settings → Merge requests → Merge request approvals section
2. Show the "Add approval rule" button in a disabled state (grayed out, non-clickable)
3. Provide a clear explanatory tooltip on hover that explains why this option is not available for the user:
   • In this situation, a statement like this could be displayed: "Approval rule editing has been disabled by your GitLab administrator. Contact your admin to modify the 'Prevent editing approval rules' setting in Admin Area."
   • Another statement could be displayed if the user doesn't have sufficient role permissions.