Create role approver dropdown

What does this MR do and why?

Describe in detail what your merge request does and why.

Create role approver dropdown

• create new role_select component
• ensure creating and editing policies with role approvers works as expected
• add tests

Screenshots or screen recordings

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

Scenario	Screenshot
New role option
Group-level with new approvers
Project-level with existing approvers

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. Enable the :scan_result_role_action feature flag with the below command

echo "Feature.enable(:scan_result_role_action)" | rails c

1. Navigate to http://gdk.test:3443/flightjs/Flight/-/security/policies/new?type=scan_result_policy
2. Verify a user can select a Role in the Actions area and the policy preview is updated with the role under roler_approvers
3. Navigate to http://gdk.test:3443/groups/flightjs/-/security/policies/new?type=scan_result_policy
4. Verify a user can select a Role in the Actions area and the policy preview is updated with the role under roler_approvers

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 #377863 (closed)

Related to #379058 (closed)