feat(bigqueryconnection): add configuration block to google_bigquery_connection

[modular-magician]

Description

This PR adds support for the configuration block (ConnectorConfiguration) to the google_bigquery_connection resource. This enables users to create BigQuery connections using the new Connector framework, which supports AlloyDB, Cloud SQL (MySQL/PostgreSQL), and other connector types.

Background

The BigQuery Connection API v1 supports AlloyDB connections via the ConnectorConfiguration framework (with connector_id: "google-alloydb"), which is a fully typed schema in the Discovery API. However, the Terraform provider currently only supports the legacy connection types (cloud_sql, aws, azure, cloud_spanner, cloud_resource, spark) and does not support the newer configuration field.

Changes

• Added configuration block to google_bigquery_connection resource in Connection.yaml
  • connector_id (required, immutable) - e.g., google-alloydb
  • endpoint - host/port configuration
  • authentication - username/password or service account
  • network - Private Service Connect configuration
  • asset (required) - database and Google Cloud resource reference
• Added configuration to exactly_one_of constraint for all existing connection types
• Added custom flatten template for authentication (password is redacted by the API on read)
• Added example/test for AlloyDB connection using configuration block

Example Usage

resource "google_bigquery_connection" "alloydb" {
  connection_id = "my-alloydb-connection"
  location      = "us-central1"

  configuration {
    connector_id = "google-alloydb"
    asset {
      database              = "mydb"
      google_cloud_resource = "//alloydb.googleapis.com/projects/my-project/locations/us-central1/clusters/my-cluster/instances/my-instance"
    }
    authentication {
      username_password {
        username = "user"
        password {
          plaintext = "password"
        }
      }
    }
  }
}

Release Note

bigqueryconnection: added `configuration` block to `google_bigquery_connection` resource to support AlloyDB and other connector types via the BigQuery Connector framework

Fixes: hashicorp/terraform-provider-google#18663

Derived from GoogleCloudPlatform/magic-modules#17083