Starting Thursday, July 23, a musical comedy made famous by Carol Burnett is taking the stage in Tenino, offering audiences a whimsical escape to a far off-place, many moons ago. Tenino Young-at-Heart Theatre’s summer musical, “Once Upon a Mattress,” is a comedic adaptation of the Hans Christen Andersen fairytale “The Princess and the Pea” that first premiered in 1959. “Carried on a wave of wonderful songs, by turns hilarious and raucous, romant…