Options to Provision Postgres via Crossplane in the autodevops pipeline

This MR allows options for postgres provisioning via crossplane.

(Based on the discussion from gitlab-org&1866 (comment 228944981))

Addition of the options postgres.managed=true postgres.managedClass="specific class name"

to allow the user choice of postgres deployment orchestrated via crossplane.

Related issue: gitlab-org/gitlab#34702 (closed)