Make internal Prometheus listen_address available to Rails app

Problem to solve

The Rails app does not know the listen_address of the internal Prometheus server (https://docs.gitlab.com/ee/administration/monitoring/prometheus/).

The Rails app needs the listen_address in order to automatically connect the self-monitoring project to the internal Prometheus server.

Epic: &1610 (closed)

Intended users

Further details

Proposal

Copy the prometheus['listen_address'] Omnibus setting into gitlab.yml.

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

Links / references