Port prometheus health check to cluster integration

What does this MR do and why?

Ports the in-cluster prometheus health check functionality to the cluster integrations. This worker has never been used (see #322581 (closed)), so it can be safely renamed. We are renaming instead of removing because ~"group::monitor" still has plans to enable the worker.

I'll make the change to enable the worker in an immediate follow-up MR. That way, if the worker has problem, we can revert just the cron addition instead of the integrations port. I

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.

Database migration output

➜  gitlab git:(port-prometheus-health-check-to-integrations) ✗ bin/rails db:migrate:up VERSION=20211008193137
== 20211008193137 AddHealthStatusColumnOnClustersIntegrationPrometheus: migrating 
-- add_column(:clusters_integration_prometheus, :health_status, :smallint, {:limit=>2, :default=>0, :null=>false})
   -> 0.0033s
== 20211008193137 AddHealthStatusColumnOnClustersIntegrationPrometheus: migrated (0.0034s) 

➜  gitlab git:(port-prometheus-health-check-to-integrations) ✗ bin/rails db:migrate:down VERSION=20211008193137
== 20211008193137 AddHealthStatusColumnOnClustersIntegrationPrometheus: reverting 
-- remove_column(:clusters_integration_prometheus, :health_status, :smallint, {:limit=>2, :default=>0, :null=>false})
   -> 0.0024s
== 20211008193137 AddHealthStatusColumnOnClustersIntegrationPrometheus: reverted (0.0045s)