Validate driver matches database type

[jackwotherspoon]

The behavior where someone passes a valid instance connection name for a Cloud SQL instance but for the wrong driver is slightly ambiguous currently. (ex. instance connection name for a Cloud SQL Postgres instance but with pymysql driver)

We should make an enum mapping drivers to database type and verify that the driver being used is correct before attempting a connection. This way we can throw a helpful error message to users pointing at the wrong instance.

We are already returning the database version as part of the metadata request so this should be pretty straightforward.

cloud-sql-python-connector/google/cloud/sql/connector/refresh_utils.py

Lines 110 to 114 in 25a740a

	metadata = {
	"ip_addresses": ip_addresses,
	"server_ca_cert": ret_dict["serverCaCert"]["cert"],
	"database_version": ret_dict["databaseVersion"],
	}