Migrate admin settings metrics and profiling page to Vue 3

What does this MR do and why?

Adds vue3_migrate_admin_metrics_and_profiling . Admin settings pages are typically haml, but there are a few small Vue apps in http://gdk.test:3000/admin/application_settings/metrics_and_profiling , hence the need for its own feature flag. One of those apps (in logging fields) is currently under its own FF (wip).

References

#634224 (closed)

#634491

Screenshots or screen recordings

After

How to set up and validate locally

1. Enable in rails console

   Feature.enable(:vue3_migrate_admin_metrics_and_profiling)
   Feature.enable(:logging_field_variant_versioning)
   

2. Restart gdk

3. Navigate to /admin/application_settings/metrics_and_profiling and change Logging Fields setting.

4. Usage Statistics also has a conditional Vue app which depends on having a Service Ping payload. The page only renders the Preview and Download buttons when a payload exists (app/views/admin/application_settings/_usage.html.haml). Otherwise it shows a warning: "Service Ping payload not found in the application cache". That warning should be where the buttons would be.

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Related to #634224 (closed)