Render WAF statistics

What does this MR do?

Part of WAF statistics reporting.

This adds a WAF statistics summary component and a chart for viewing the history of WAF traffic.

In addition, this:

• Updates the expected response structure from the WAF statistics endpoint, according to the latest from !19789 (closed).
• Removes the link from the popover per this discussion.
• Removes pushing the threat_monitoring feature flag to the frontend, since it wasn't being read anyway, and the controller itself is guarded behind the flag, which is sufficient.

This work lives behind the disabled-by-default threat_monitoring feature flag.

Screenshots

These were created by applying this patch to mock the endpoint responses, and also enabling the threat_monitoring feature flag.

Context	Before	After
Page
Popover

Loading/loaded states

Loading	Loaded

Demo video

threat_monitoring_updated-clipped

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 - Will do this when the MVC is nearer completion.