Add validation coloring on approvers

What does this MR do and why?

Add validation coloring on approvers

• add red outline if an error occurs with not enough approvers selected
• follow convention for adding valid outline

Changelog: added

EE: true

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Scenario	Before	After
Picture	-
Video	approver_invalid_-_b	approver_invalid_-_a

How to set up and validate locally

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

1. Upload a GitLab Ultimate license
2. Navigate to a project/group => Secure => Policies => New policy => Scan Result Policy
3. Add a name to the policy
4. Set the scan type to Security
5. Change number of approvers to 10
6. Add a role approver and had Owner
7. Submit the policy
8. Verify the number of approvers input AND the approver input are outlined in red and the error says it is invalid
9. Add an individual approver
10. Verify the invalid outline is removed
11. Submit the policy
12. Verify the number of approvers input AND the approver inputs (both) are outlined in red and the error says it is invalid
13. Add another individual approver, navigate to yaml mode, and submit the policy
14. Verify the error says it is invalid
15. Switch to rule mode and change the number of approvers to 2
16. Verify the invalid outline is removed
17. Submit the policy
18. Ensure the policy submits

MR acceptance checklist

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

• I have evaluated the MR acceptance checklist for this MR.

Related to #395545 (closed)