Update Prometheus documentation with deployment namespacing requirement

What does this MR do?

Default dashboard for projects environment is making assumption upon kubernetes namespaces into which this environment is deployed. In order to make prometheus queries for ingress to work correctly, environment need to be deployed into kubernetes namespaces as described in KUBE_NAMESPACE

This requirement is not mentioned in documentation, which may confuse users and stop them from fully utilizing auto monitoring.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Documentation (if required)

Reports #33304 (closed)