A migrant at the newly opened shelter in Brooklyn’s popular McCarren Park raved to The Post on Tuesday life is good — with three hot meals a day, spacious clean living quarters and use of the leafy refuge’s pool. “They treat us very well,” said Miguel Mujica, a 39-year-old dad of two from Venezuela. “There’s nothing they stop us from doing.” Mujica has been staying at the McCarren Play Center in trendy Williamsburg since Saturday, a day after the city set up 100 military cots for asylum-seekers there to help take pressure off city shelters that are bursting at the...