easy enablement for prometheus related feature

[SamYuan1990]

Summary

Easy enablement for prometheus feature by environment variables

Desired Behaviour

For sample as COUCHDB_USER, as a user, I want to enable prometheus related feature by environment value as

[prometheus]
additional_port = false
bind_address = 127.0.0.1
port = 17986

prometheus_additional_port prometheus_bind_address prometheus_port

Possible Solution

Not sure if https://github.com/apache/couchdb/blob/main/configure#L247 this line is useless. if not, take prometheus_port as sample:

{prometheus_port, $prometheus_port}

and in rel/overlay/etc/default.ini

[prometheus]
additional_port = false
bind_address = 127.0.0.1
port = {{prometheus_port}}

Additional context

N/A

[SamYuan1990]

as so far, with default value as configuration. access:

/tmp % curl 127.0.0.1:5984/_node/_local/_prometheus 
{"error":"unauthorized","reason":"You are not a server admin or read-only metrics user"}

related with https://github.com/apache/couchdb/discussions/3935

I can understand we want to disable the prometheus by default, but... as current status, the prometheus seems enabled at port 5984, and blocked prometheus as prometheus operator to access it. are we want it disabled by default? or we'd better have a fixable configuration to control this feature enablement?

with my hands on, I am confusing.

attachment my yaml file for reference.

---
apiVersion: v1
kind: Service
metadata:
  name: org1peer1couchdb
spec:
  selector:
    app: org1peer1couchdb
  ports:
  - name: couchport
    port: 5984
    protocol: TCP
  - name: matrix
    port: 17986
    protocol: TCP  
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: org1peer1couchdb
spec:
  replicas: 1
  selector:
    matchLabels:
      app: org1peer1couchdb
  template:
    metadata:
      labels:
        app: org1peer1couchdb
    spec:
      containers:
      - name: couchdb
        image: couchdb:3.2
        imagePullPolicy: IfNotPresent
        env:
          - name: "COUCHDB_USER"
            value: "admin" 
          - name: "COUCHDB_PASSWORD"
            value: "adminpw"
          - name: "PROMETHEUS_ADDITIONAL_PORT" # useless so far
            value: "true"
          - name: "PROMETHEUS_BIND_ADDRESS" # useless so far
            value: "0.0.0.0"
          - name: "PROMETHEUS_PORT" # useless so far
            value: "17986"
        ports:
            - containerPort: 5984
            - containerPort: 17986
---
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  name: org1peer1couchdb
  namespace: default
  labels:
    release: mypro
spec:
  namespaceSelector: 
    matchNames:
    - default
  selector:
    matchLabels:
      app:  org1peer1couchdb
  endpoints:
  - port: couchport 
    path: /_node/_local/_prometheus