The central city and any one or more towns, cities or boroughs, in addition to such powers as each has under any provision of the general statutes or any special act, may adopt and amend a charter for the metropolitan district, which charter shall, among other things, provide for the structure and organization of the metropolitan district government, the powers and duties of such government, the means of financing its operations, the admission of additional towns, cities and boroughs as members of the metropolitan district, the withdrawal of any constituent municipality and the dissolution of such district. Said charter shall supersede any existing charter provisions and all special acts inconsistent with the provisions of the metropolitan district charter. In addition, such district, unless prohibited by the provisions of its charter, shall have such powers as are granted to any of its constituent towns, cities and boroughs under the Constitution, general statutes or special acts.