Notwithstanding any restrictions contained in a city charter, any power, privilege, or authority exercised or capable of exercise by a public agency of this state may be exercised and enjoyed jointly with any other public agency of this state and jointly with any public agency of any other state or of the United States to the extent that laws of such other state or of the United States permit such joint exercise or enjoyment. Any agency of state government when acting jointly with any public agency may exercise and enjoy all of the powers, privileges, and authority conferred by the Joint Public Agency Act upon a public agency.