Update default CouchDB tag to 3.2.0 and expose Prometheus support.

[sag]

What this PR does / why we need it:

Bump CouchDB version to 3.2.0

CouchDB 3.2.0 adds built-in prometheus style metrics. These metrics are exposed at /_node/_local/_prometheus. Since this is part of the main http server, this endpoint is authenticated. CouchDB 3.2.0 Also adds configuration to expose the new metrics on another unauthenticated port. This PR also adds extra support for that new configuration.

New Variables

New variables that match the new CouchDB configuration have been added. prometheusPort.enabled - when true the new feature will be enabled prometheusPort.port - the new unauthenticated port prometheusPort.bind_address - the address to listen on

When prometheusPort.enabled is true:

• A new prometheus.ini is added to the /defaults.d directory
• A metrics port is added to the headless service
• The new metrics port is opened up in the NetworkSecurityPolicy
• The new metrics port is exposed on the CouchDB container

This makes it possible to have prometheus scrape CouchDB metrics using a ServiceMonitor such as

apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  name: couchdb
  labels:
    release: prometheus-stack
spec:
  selector:
    matchLabels:
      app:  couchdb
  endpoints:
  - port: metrics 
    path: /_node/_local/_prometheus

Referenced URLS:

• https://docs.couchdb.org/en/latest/api/server/common.html#api-server-prometheus
• https://docs.couchdb.org/en/latest/config/misc.html#configuration-of-prometheus-endpoint

Special notes for your reviewer:

Checklist

• [x] Chart Version bumped
• [x] e2e tests pass
• [x] Variables are documented in the README.md
• [x] Chart tgz added to /docs and index updated

[kocolosk]

Thanks for this contribution! It looks quite nice, happy to merge it.