pgbouncer extension points

[benbz]

e.g. setting in values.yaml:

pgbouncer:
  env:
  - name: SERVER_TLS_SSLMODE
    value: require
  extraVolumeMounts:
  - name: config
    mountPath: /etc/pgbouncer
  extraVolumes:
  - name: config
    emptyDir: {}

now results in server_tls_sslmode = require in pgbouncer.ini and uses an emptyDir rather than writing files in the container. This is useful for OpenShift as the entrypoint script can't write files to /etc/pgbouncer. It is not sufficient on its own - a custom entrypoint script or pgbouncer.ini is also required so that user = postgres is replaced with user = as per edoburu/docker-pgbouncer#23

[tiina303]

Thanks for improving our charts 😃