[DPE-7726] Use Patroni API for is_restart_pending() (instead of SQL select from pg_settings)

lib/charms/postgresql_k8s/v1/postgresql.py

@@ -255,8 +255,10 @@ def _connect_to_database(
              psycopg2 connection object.
         """
         host = database_host if database_host is not None else self.primary_host
+        dbname = database if database else self.database
+        logger.debug(f"New DB connection: dbname='{dbname}' user='{self.user}' host='{host}' connect_timeout=1")
         connection = psycopg2.connect(
-            f"dbname='{database if database else self.database}' user='{self.user}' host='{host}'"
+            f"dbname='{dbname}' user='{self.user}' host='{host}'"
             f"password='{self.password}' connect_timeout=1"
         )
         connection.autocommit = True
@@ -1267,23 +1269,6 @@ def update_user_password(
             if connection is not None:
                 connection.close()
 
-    def is_restart_pending(self) -> bool:
-        """Query pg_settings for pending restart."""
-        connection = None
-        try:
-            with self._connect_to_database() as connection, connection.cursor() as cursor:
-                cursor.execute("SELECT COUNT(*) FROM pg_settings WHERE pending_restart=True;")
-                return cursor.fetchone()[0] > 0
-        except psycopg2.OperationalError:
-            logger.warning("Failed to connect to PostgreSQL.")
-            return False
-        except psycopg2.Error as e:
-            logger.error(f"Failed to check if restart is pending: {e}")
-            return False
-        finally:
-            if connection:
-                connection.close()
-
     def database_exists(self, db: str) -> bool:
         """Check whether specified database exists."""
         connection = None