If it seems like actor Dwayne “The Rock” Johnson is ubiquitous and might run for president one day, well, there’s an NBC sitcom for that called “Young Rock.” The comedy returned this week for a sophomore year where three actors play younger versions of Johnson while Johnson plays a future version of himself in 10 years running for president. The concept is audacious but the result feels like ABC’s flashback coming-of-age show “Fresh Off the Boat” in general tone. That may be because two of the executive producers ― Nahnatchka Khan and Jeff Chiang ― oversaw “Fresh Off the Boat.” “We want it to …