Add to Go operator support for db stores

[tmihalac]

Is your feature request related to a problem? Please describe. The current feast go operator doesn't support db stores for the various components(online,offline,registry)

Describe the solution you'd like The proposed solution is to add to the operator the ability to read the DB parameters from a secret specified in the CR

kind: FeatureStore
metadata:
  name: example
spec:
  feastProject: my_project
  services:
    onlineStore:
      persistence:
        store:
          type: postgres
          secretRef: 
            name: _SECRET_NAME_ 
          secretKeyName: my-postgres