Add new Connect prometheus endpoint

[tnederlof]

With the release of Connect 2024.02.0, there is a documented Prometheus endpoint that the Connect chart should add in support for. Note currently this (https://docs.posit.co/connect/admin/operational-metrics/#included-metrics) is the list of metrics that does not cover the existing graphite metrics. For this reason it might make the most sense to expose the new metrics in ServiceMonitor alongside the Graphite exporter.

Listing out some changes that may need to be made:

• Setting Metrics.PrometheusListen in the default config
• Adding a named port (metrics is already in use so will need a different name) in the Connect service to the value of Metrics.PrometheusListen
• Add a new entry to ServiceMonitor to pick up the new named port

[tnederlof]

Closed by https://github.com/rstudio/helm/pull/516