Allow Private Service Connect (PSC) for CloudSQL auth integration

[shinji62]

Is your feature request related to a problem? Please describe.

I want to use Vault to generate credentials for Cloudsql (postgres) the instances is in a different VPC/Project than Vault, as VPC Peering and others are not possible (overlapping CIDR) the CloudSQL instances is available with Private Service Connect.

As well those options are not supported for MySQL, so I would like to add those options to MySQL as well.

Describe the solution you'd like Connect to Cloud Postgres instances with IAM using the PSC endpoint

Describe alternatives you've considered We can use static credentials to connect the CloudSQL.

Extra Information: CloudSQL connector support the WithPSC options out of the box, so I think the PR would be similar to https://github.com/hashicorp/vault/pull/26828

I am happy to contribute if you are agree to proceed.