Change Postgres config using Kubernetes configMap

Question

I'm trying to deploy postgres using Kubernetes. This step works well.

But now I need to customised the pg_hba.conf file. So the idea is to use a configMap to mount the personal file.

Here are my deployment file:

apiVersion: v1
kind: ConfigMap
metadata:
  name: pg-hba-configmap
data:
  pg_hba.conf: |+
    # TYPE  DATABASE        USER                ADDRESS            METHOD
    # Some personal  settings here

---

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: db
spec:
  selector:
    matchLabels:
      app: db
  serviceName: db
  replicas: 1
  template:
    metadata:
      labels:
        app: db
    spec:
      nodeSelector:
        db: 'true'
      containers:
      - name: db
        image: kartoza/postgis:10.0-2.4
        volumeMounts:
        - name: data-volume
          mountPath: /var/lib/postgresql
        - name: pg-hba-config-volume
          mountPath: /var/lib/postgresql/10/main/pg_hba.conf
          subPath: pg_hba.conf
      volumes:
      - name: data-volume
        hostPath:
          path: /data/db
      - name: pg-hba-config-volume
        configMap:
          name: pg-hba-configmap

But this doesn't work. The db is in Error state. In logs, I can see this:

chown: changing ownership of '/var/lib/postgresql/10/main/pg_hba.conf': Read-only file system

Also, on the server where is mounted the database, I only have this:

root@server:/data/db/10/main# ls -l
total 0
-rwxr-xr-x 1 root root 0 Oct  8 08:49 pg_hba.conf

I should have all the database here. It's like if all the folder was overwritten.

What am I doing wrong here and how can I mount my customised config ?

Thanks