Document updating of DB name/DB user is not supported.

[sangee2004]

1. Deploy postgres service.
2. Attempt to update DB name/DB user.

This results in postgres service stuck in "not ready" state forever

acorn apps
NAME              IMAGE                                COMMIT         CREATED   ENDPOINTS                                                               MESSAGE
consume-postgre   f7b3d0d049b9                         2588b65ca76c   18m ago   https://consume-postgre-05b44351.wcovwb.on-acorn.io                     (container: app): waiting for service to be ready [db]; (service: db): not ready
mypostgresql      ghcr.io/acorn-io/postgres:v15.3-1*   2588b65ca76c   22m ago                                                                           (container: postgres): not ready; (service: db): not ready

Logs :

postgres-d557b6bf9-95q6l: PostgreSQL Database directory appears to contain a database; Skipping initialization
postgres-d557b6bf9-95q6l: 
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:17.307 UTC [1] LOG:  starting PostgreSQL 15.3 on x86_64-pc-linux-musl, compiled by gcc (Alpine 12.2.1_git20220924-r10) 12.2.1 20220924, 64-bit
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:17.307 UTC [1] LOG:  listening on IPv4 address "0.0.0.0", port 5432
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:17.307 UTC [1] LOG:  listening on IPv6 address "::", port 5432
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:17.314 UTC [1] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:17.323 UTC [24] LOG:  database system was shut down at 2023-12-08 23:02:12 UTC
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:17.334 UTC [1] LOG:  database system is ready to accept connections
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:26.297 UTC [34] FATAL:  role "postgres2" does not exist
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:36.273 UTC [47] FATAL:  role "postgres2" does not exist
postgres-d557b6bf9-95q6l: 2023-12-08 23:02:36.282 UTC [48] FATAL:  role "postgres2" does not exist

If this use case is not supported , we should document that updating of DB name/DB user is not supported.