Persist Threat Monitoring alert dismissal

What does this MR do?

Persist Threat Monitoring alert dismissal

This ensures that once a user dismisses the info alert on the Threat Monitoring page, it doesn't appear again on subsequent visits.

Part of WAF statistics reporting.

TODO

• Once !21916 (merged) is merged, rebase and retarget this to master (which is why this is currently WIP)

Screenshots

Note: since the backend isn't done yet, and that this is based on !21916 (merged), these screenshots can only be recreated by first applying this patch: mock_threat_monitoring_apis.patch (apply with git apply <patchfile>)

Not dismissed	Dismissed

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

ee/spec/frontend/security_dashboard/components/project_list_spec.js

@@ -93,7 +93,7 @@ describe('Project List component', () => {
 
     factory({ projects: mockProjects, stubs: { GlButton } });
 
-    getFirstRemoveButton().trigger('click');
+    getFirstRemoveButton().vm.$emit('click');
 
     return wrapper.vm.$nextTick().then(() => {
       expect(wrapper.emitted('projectRemoved')).toHaveLength(1);