WHAT
Review the work already spiked for Postgres Creation.

Implement any missing logic for Creation of a Postgres is GCP

We should aim to follow a similar patter where the CreateConfig is mapped to a CreateDBInput param in the GCP package. See here for example -> https://github.com/integr8ly/cloud-resource-operator/blob/master/pkg/providers/aws/provider_postgres.go#L836-L923

Implement unit tests for the new functions added

HOW
Review changes in working branch linked in the epic brief for functinoality around creating a postgres in GCP and creating the connection secret for the DB. 

TESTS
Unit tests added

DONE
Postgres Creation functionality in GCP that matches AWS implementation