Platform RDS: aws-broker dev, stage, prod

[rcgottlieb]

In order to get out of postgres 12 before AWS End of Standard Support, we want to update the postgres database for concourse credhub staging

Acceptance Criteria

• Database upgraded to Postgres 16.1
• concourse staging still works, and acceptance tests
• Terraform updated and plans show nothing new

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Security considerations

This improves our security by having a postgres that gets updates :)

Implementation sketch

• Use the aws UI to select the targeted RDS instance, perform the upgrade using the UI for dev of whatever, this will include the parameter group
• Update the aws-broker piece for whatever module ^^ lives and add or override whatever value is in rds_db_engine_version for that module.
• Run the terraform plan through the pipeline, if step 1 and 2 was done correctly, it should be seen as a no-op for Prod

[rcgottlieb]

This is done by fixing the acceptances tests, and modifying the laboratory repo with this PR: cloud-gov/laboratory#16

This is the PR for modifying the Postgres versions: cloud-gov/aws-broker#378