New York taxpayers will dole out $20 million a month to house migrants on Randall’s Island, according to a state source — or $10,000 per asylum-seeker if the site fills all of its 2,000 beds.The makeshift facility off Manhattan is one of four migrant housing sites fully funded by the state as part of a desperate effort to keep up with the flood of migrants who have New York City at its breaking point.A well-placed source with the state told The Post over the weekend that the state is providing $20 million a month to run the Randall’s center.New York...