Refactor Postgres template settings

[jgwerner]

Refactor template settings to avoid repetition between connection settings related to an internally deployed Postgres pod and the connection settings related to external Postgres instances.

All Postgres connection URIs should assume that the Postgres instance is running independently, regardless of whether the instance is running as a pod or with an externally managed service, such as AWS RDS.

[jgwerner]

@Abhi94N let's review this issue in conjunction with #56

[jgwerner]

Related to #53 #54

[jgwerner]

@Abhi94N we can just document the values.yaml file to reference Bitnami's PostgreSQL helm chart with the differences between postgresqlPostgresPassword and postgresqlPassword.