Those glamorous people you see in the upscale boutiques of Beverly Hills and Santa Monica may have a secret beyond their romantic lives and surgical histories. Many of these fashionable glitterati — squeezed out of palatial homes they'd bought on debt — may have just put their rent checks in the mail. Renting now makes sense in many markets — even for the very prosperous. Kami Merabi, president of L.A.- based realtor Merabi & Sons, says he