Add note about in-cluster postgres limitations on Software

[jwitz]

Issue Type

Inaccurate, misleading, or out-of-date information

Links to Affected Docs

https://docs.astronomer.io/software/install-gcp et al

The Issue or Context

We need to mention lack of in-cluster postgres support for all clouds, not just Azure.

If you provision an external database, postgresqlEnabled should be set to false in Step 8. The in-cluster database should be used only for development or proof-of-concept installations. All production installations should use an external database.

Fix or Proposed Change

No response

Additional Notes

No response

Required Reviewers

No response