Without increasing local taxes, and in a manner consistent with Sonoma County's General Plan and zoning ordinance, shall public bodies be authorized to develop, construct, or acquire housing units affordable to low-income persons, including elderly and disabled persons, within the County's unincorporated area, either directly or by assisting private projects, in an annual amount not exeeding one-half of one percent (1/2%) of the housing units existing in the unincorporated area in that year?