Disable custom role delete button for sec policy

What does this MR do and why?

Disable custom role delete button for sec policy

• if a custom role is used in a security policy, then it should not be able to be deleted
• disable delete button if it is used in a security policy on the frontend
• show popover with policies

References

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MR acceptance checklist

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Screenshots or screen recordings

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Scenario	Screenshot
No policy associated to custom role - group
Has policies associated to custom role - instance
Has no policies associated, but has member assigned - instance

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Admin

1. Upload a GitLab Ultimate license
2. Ensure your local environment is set up for self-managed (e.g. export GITLAB_SIMULATE_SAAS=0 && gdk restart)
3. Create a custom role at the admin level (e.g. Admin => Settings => Roles and permissions)
4. Enable the custom role feature flag echo "Feature.enable(:security_policy_custom_roles)" | rails c
5. Navigate to a group/project => Secure => Policies => New policy => Merge request approval policy => Create a policy with a custom role in it
6. Navigate back to the custom role and try to delete it
7. Verify it can not be delete and a tooltip shows with the policies it is being used in

Top-level group

1. Upload a GitLab Ultimate license
2. Ensure your local environment is set up for SaaS (e.g. export GITLAB_SIMULATE_SAAS=1 && gdk restart)
3. Create a custom role in a top-group level group that you are an owner of (e.g. Group => Settings => Roles and permissions)
4. Enable the custom role feature flag echo "Feature.enable(:security_policy_custom_roles)" | rails c
5. Navigate to a group/project => Secure => Policies => New policy => Merge request approval policy => Create a policy with a custom role in it
6. Navigate back to the custom role and try to delete it
7. Verify it can not be delete and a tooltip shows with the policies it is being used in

Related to #510191 (closed)