Update Ansible Role to prometheus.prometheus

[jlosito]

The cloudalchemy.prometheus Ansible role has been set as a public archive and has been deprecated in favor of the prometheus.prometheus role. The documentation still links to the deprecated cloudalchemy.prometheus role and should be updated.

It looks like this has been updated already but hasn't been deployed to the live site. https://github.com/jlosito/prometheus/blob/main/docs/installation.md#ansible