Limit editing of approval rules in Branch rule details

What does this MR do and why?

Describe in detail what merge request is being backported and why

Backporting !156023 (merged) to hide exposed editing of MR approval rules on the Branch rule details page. Until edit_branch_rules feature flag is set to false, this section should only be a read-only, as it is still under development, is not fully functioning and contains a know UI bug ( #456976 (closed))

MR acceptance checklist

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

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:package-and-test-ee job has either succeeded or been approved by a Software Engineer in Test.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
• Ask questions on the #releases Slack channel (internal only).

Related to #466705 (closed)