### Apache Airflow Provider(s)

google

### Versions of Apache Airflow Providers

apache-airflow-providers-google~=5.0

### Apache Airflow version

2.1.3 (latest released)

### Operating System

MacOS Big Sur

### Deployment

Astronomer

### Deployment details

_No response_

### What happened

The CloudSqlProxyRunner queries the Airflow DB directly to retrieve the GCP connection.

https://github.com/apache/airflow/blob/7b3a5f95cd19667a683e92e311f6c29d6a9a6a0b/airflow/providers/google/cloud/hooks/cloud_sql.py#L521

### What you expected to happen

In order to not break when using connections stored in external secrets backends, it should use standardized methods to retrieve connections and not query the Airflow DB directly.

### How to reproduce

Use a CloudSQLDatabaseHook with `use_proxy=True` while using an external secrets backend.

### Anything else

Every time

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

airflow/providers/google/cloud/hooks/cloud_sql.py
self.sql_proxy_version = self.extras.get('sql_proxy_version')  
        self.sql_proxy_binary_path = self.extras.get('sql_proxy_binary_path')  
        self.user = self.cloudsql_connection.login  
        self.password = self.cloudsql_connection.password  
        self.public_ip = self.cloudsql_connection.host  
        self.public_port = self.cloudsql_connection.port  
        self.sslcert = self.extras.get('sslcert')  
        self.sslkey = self.extras.get('sslkey')  
        self.sslrootcert = self.extras.get('sslrootcert')  
        
        self.sql_proxy_tcp_port = None
        self.sql_proxy_unique_path = None  
        self.db_hook = None  
        self.reserved_tcp_socket = None  
        
        
        self.db_conn_id = str(uuid.uuid1())
        self._validate_inputs()
    @staticmethod
    def _get_bool(val: Any) -> bool:
        if val == 'False':
            return False
        return True
    @staticmethod
    def _check_ssl_file(file_to_check, name) -> None:
        if not file_to_check:
            raise AirflowException(f"SSL connections requires {name} to be set")
        if not os.path.isfile(file_to_check):
            raise AirflowException(f"The {file_to_check} must be a readable file")
    def _validate_inputs(self) -> None: