Fix: Postgres read-replica "psc_enabled" change never set

[philoj]

The psc_config dynamic block in resource google_sql_database_instance.replicas keeps getting removed by the planner while the defaults are always present.
This pull request keeps the block with default values when PSC is disabled inside the replica.
No functional changes. Keeps the plan tidy, that's all

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[imrannayer]

@philoj this is provider issue. Provider should be able to ignore permadiff for nulls. We can put this workaround in module for the time being.

[imrannayer]

/gcbrun

[philoj]

@philoj this is provider issue. Provider should be able to ignore permadiff for nulls. We can put this workaround in module for the time being.

Didn't know that 🙂. Thank you

[sofuture]

This change seemed to cause a permadiff for those fields, for my configuration at least.