Add Cloud SQL Auth Proxy IAM authentication

[nailo2c]

closes: #35347

How

Add the sql_proxy_enable_iam_login parameter to support -enable_iam_login in CloudSqlProxyRunner.

What

Reproducer DAG:

import os
from datetime import datetime

from airflow import DAG
from airflow.providers.google.cloud.operators.cloud_sql import CloudSQLExecuteQueryOperator

DAG_ID = "cloudsql_proxy_iam_reproduce"
GCP_CONN_ID = os.environ.get("AIRFLOW_35347_GCP_CONN_ID", "google_cloud_default")
CLOUDSQL_CONN_ID = os.environ.get("AIRFLOW_35347_CLOUDSQL_CONN_ID", "cloudsql_proxy_iam_postgres")

with DAG(
    dag_id=DAG_ID,
    schedule=None,
    start_date=datetime(2026, 1, 1),
) as dag:
    CloudSQLExecuteQueryOperator(
        task_id="query_cloudsql_with_proxy_iam",
        gcp_conn_id=GCP_CONN_ID,
        gcp_cloudsql_conn_id=CLOUDSQL_CONN_ID,
        sql=["SELECT 1"],
    )

Connection:

{
	"conn_type": "gcpcloudsql",
	"login": "<your-sa-name>@<your-project>.iam.gserviceaccount.com",
	"password": "",
	"host": "127.0.0.1",
	"port": 5432,
	"schema": "test_db",
	"extra": {
		"database_type": "postgres",
		"project_id": "<your-project>",
		"location": "us-central1",
		"instance": "<your-instance-name>",
		"use_proxy": "True",
		"sql_proxy_use_tcp": "True",
		"sql_proxy_enable_iam_login": "True"
	}
} 

Before fix

After fix

System test

Cloud SQL instance lifecycle (create → delete) executed as expected.

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