FE: Add ability to have multiple actions

Why are we doing this work

• Users want to be able to select a combination of roles, individual users, and groups to be approvers

Relevant links

• Design Issue
  • 

Implementation plan

MR 1

• frontend in scan_result_policy_editor.vue
  • Conditionally render a + Add new approver button to add an additional action based on the :scan_result_role_action feature flag (similar to in scan_execution_policy_editor.vue
• frontend in .../security_orchestration/components/policy_editor/scan_result_policy/policy_action_builder_v2.vue
  • frontend update the action builder to take the action index and make changes on the correct action
  • frontend add a remove button (similar to scan_execution_policy/policy_action_builder.vue#L147)
  • frontend only allow one action per type (one role action, one user action, one group action)
  • frontend ensure that when a user changes the type selection, the selection is cleared

Verification steps

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

3. Navigate to a project/group => Security & Compliance => Policies => New policy => Scan Result Policy
4. Verify a user can add multiple actions and modify individual actions that do not affect the other actions