Ability to reference adminpw / databases as a secret #14

There are values in the main config (pgdog.toml) that are sensitive and should not be displayed as ConfigMaps, should one choose to do so: namely the admin password and the various database settings (in case we need to enter db passwords there if we're not using auth passthrough).

As an aside, it is currently possible to use the ExternalSecrets feature to load a secret even if one is not using the ExternalSecrets operator, with something like

externalSecrets:
  enabled: true
  create: false
  secretName: "pgdog-users"

which is nice if you just wanna use an externally provided vanilla k8s secret; could this be documented and/or guaranteed to continue functioning in the future (AKA not introduce a hard dependency on ESO for this)?