Support Swithcover for MySQL and PostgreSQL

[modular-magician]

• References

  • issue: Implement new cloud SQL API switchover #18807
  • work for SQL server: Support SQL Server Switchover (after resolving email rebase conflicts) GoogleCloudPlatform/magic-modules#12241
  • design (google only): go/speckle-switchover-terraform-proposal

• Implementation

  • main change: adding replication_cluster: just copied corresponding filed from API. https://cloud.google.com/sql/docs/mysql/admin-api/rest/v1beta4/instances#resource:-databaseinstance . dr_replica is read only, and failover_dr_replica_name is optionally set by customer. To support "deletion" of optional computed resource, we use "NON_EXISTENT" as placeholder for non-existent failover_dr_replica_name in terraform.

  • isSwitchoverRequested(): just removed restriction on the database type.

  • isSwitchoverFromOldPrimarySide() also removed restriction on the database type, and checking isCascadableReplica only for SQL server (because this concept is SQL server specific).

  • nit: when handling error from PromoteReplica/Swithcover, we use d.Get("name") instead of instance.Name which returns nullptr error.

• Tests

  • Added VCR tests for MySQL and PostgreSQL. They exercise end-to-end switchover CUJ.
  • Also verified that setting/unsetting failover_dr_replica_name to validate that "NON_EXISTENT" works correctly.

• Docs

  • most of changes are in mmv1/third_party/terraform/website/docs/guides/sql_instance_switchover.html.markdown I added new sections for MySQL and PostgreSQL
  • changes in mmv1/third_party/terraform/website/docs/r/sql_database_instance.html.markdown are minimal, just basic information about added fields, and summary of switchover.

Release Note Template for Downstream PRs (will be copied)

sql: added `replication_cluster` field to `google_sql_database_instance` resource

sql: added support of switchover for MySQL and PostgreSQL in `google_sql_database_instance` resource

Derived from GoogleCloudPlatform/magic-modules#12646

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