[WIP] Add support for sql_network_architecture in CloudSQL instances

[marblejenka]

For https://github.com/hashicorp/terraform-provider-google/issues/17552 .

At this time, this patch submits the following request to the endpoint,

{
  "databaseVersion": "MYSQL_8_0",
  "name": "api-test-1h0bto0bma",
  "region": "us-central1",
  "settings": {
    "activationPolicy": "ALWAYS",
    "availabilityType": "ZONAL",
    "dataDiskType": "PD_SSD",
    "edition": "ENTERPRISE",
    "enableGoogleMlIntegration": false,
    "pricingPlan": "PER_USE",
    "storageAutoResize": true,
    "tier": "db-g1-small"
  },
  "sqlNetworkArchitecture": "OLD_NETWORK_ARCHITECTURE"
}

however, results in an instance with NEW_NETWORK_ARCHITECTURE instead of OLD_NETWORK_ARCHITECTURE, without error.

s2@cloudshell:~ (s2tfdev-able-goat)$ gcloud sql instances describe api-test-1h0bto0bma | grep sqlNetworkArchitecture:
sqlNetworkArchitecture: NEW_NETWORK_ARCHITECTURE

This makes it impossible to build an instance that works with the old network architecture, causing tests to fail. Without a way to create Cloud SQL instances with the old network architecture, we are unable to implement a working test, so this patch cannot be merged at this time.

Release Note Template for Downstream PRs (will be copied)

Add support for sql_network_architecture in CloudSQL instances