THE long-awaited "Friends" cast reunion will be broadcast on May 27 and will feature a slew of celebrity guests including Justin Bieber, Lady Gaga, and K-Pop band BTS, streaming service HB0 Max has announced. "Friends: The Reunion," featuring all six of the original cast, was originally supposed to have been filmed more than a year ago but was repeatedly delayed by the coronavirus pandemic. The unscripted, one-off special was filmed earlier this year on the same sound stage in Los Angeles as the original comedy about six young 20-somethings, played by Jennifer Aniston, Lisa Kudrow, Courteney Cox, David Schwimmer, Matt…