Doc: move environment metrics to its own doc
What
Move the portion of monitoring environments (https://docs.gitlab.com/ee/ci/environments.html#monitoring-environments) to its own document.
Where
Into ce/user/project/integrations/prometheus_library/environments.md
.
Why
By looking at the UI:
This document is misplaced under /ci/
, it should be grouped with operations.
As it needs Prometheus to be used, it seems to me that its correct location is together with the other metrics doc.
When we move it to its own doc, we can add it to the global nav.
@axil WDYT?