Add group-level policy informational banner

What does this MR do and why?

Add group-level policy informational banner

• it tells the user that their group-level policy will affect all projects
• update tests

Related to #345317 (closed)

Screenshots or screen recordings

Scenario	Before	After
Group-level w/out error
Group-level w/ error
Project-level w/out error		No visual change
Project-level w/ error		No visual change

How to set up and validate locally

1. Enable :group_level_security_policies feature flag
2. Upload a GitLab Ultimate license
3. Apply the following patch

Patch

diff --git a/ee/app/assets/javascripts/threat_monitoring/policy_editor.js b/ee/app/assets/javascripts/threat_monitoring/policy_editor.js
index 01ee8e916f7..dafadb88287 100644
--- a/ee/app/assets/javascripts/threat_monitoring/policy_editor.js
+++ b/ee/app/assets/javascripts/threat_monitoring/policy_editor.js
@@ -43,7 +43,7 @@ export default (el, namespaceType) => {
 
   let component = PolicyEditorApp;
 
-  if (gon.features?.containerSecurityPolicySelection) {
+  if (true || gon.features?.containerSecurityPolicySelection) {
     component = NewPolicyApp;
   }

4. Navigate to a group => Security & Compliance => Policies => 'New policy'
5. Navigate to a project in that group => Security & Compliance => Policies => 'New policy'

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.