DOUG CRIDER Kathy Mattea, left, with Suzy Bogguss. Longtime friends Kathy Mattea and Suzy Bogguss are teaming up for a tour, titled Together at Last, that features them not with their own bands, but together, throughout the night, sharing the stage with no other musicians. It comes to the Union County Performing Arts Center in Rahway, June 4. “The first few nights I was like, ‘You mean they’re going to give me a paycheck for this?,’ ” says Mattea. ” ‘I’ve just been telling stories and hanging out with my girlfriend.’ It’s just so sweet, and we have similar enough tastes that our fans enjoy the…