add prometheus to the gitlab.rb

This enables the basic prometheus in the gitlab.rb. It allows one to enable it using

node.default['omnibus-gitlab']['gitlab_rb']['prometheus']['enable'] = true

in a wrapper cookbook.

@karcaw Thanks for the MR! Apart from prometheus, you'll probably also need

        "node_exporter",
        "redis_exporter",
        "postgres_exporter",
        "gitlab_monitor",

Would you mind adding that too?

added 1 commit

• 019ff1df - add a few more keys for exporting metrics

Compare with previous version

Added!

Thanks!

mentioned in commit 8097d165

merged