Announce Deprecation of Influx DB

We should announce deprecation of Influx DB Metrics in an upcoming release. Target remove in 13.0.

Announcement Language

Language for announcement in release post:

TBD

Tasks

• Announce in upcoming release post
• Update relevant documentation (one example)

History

We've instrumented GitLab with Prometheus as a standard. As we've gotten to parity on that instrumentation AND the available dashboards we will be removing InfluxDB support in favor of Prometheus.