[Monitoring] Make monitoring collection API public again (elastic#205190

)

Related to elastic#186882

## Summary

elastic#186781 required all teams to
make sure that all Kibana APIs in their respective plugins were using
the appropriate access `internal` or `public`.

PR elastic#186882 flagged the
`/api/monitoring_collection/{type}` API endpoint as `internal`. The
effect of that change was the [appearance of deprecation
logging](elastic#186882 (comment))
in Kibana logs, because that endpoint is called from the [`kibana`
Metricbeat
module](https://github.com/elastic/beats/blob/main/metricbeat/module/kibana/kibana.go#L42C1-L46C1)
in order to monitor Kibana.

For this reason, we need to change the access mode of that API endpoint
back to `public`.

(cherry picked from commit 52cab45)

x-pack/platform/plugins/private/monitoring_collection/server/routes/api/v1/dynamic_route/get_metrics_by_type.ts

@@ -37,7 +37,7 @@ export function registerDynamicRoute({
     {
       path: `${MONITORING_COLLECTION_BASE_PATH}/{type}`,
       options: {
-        access: 'internal',
+        access: 'public',
         authRequired: true,
         tags: ['api'], // ensures that unauthenticated calls receive a 401 rather than a 302 redirect to login page
       },