By Akane Otani NEW YORK (Reuters) – The highly anticipated debut of Alibaba Group Holding Ltd , the Chinese e-commerce group, will come amid the busiest year for initial public offerings since the technology bubble burst in 2000. Alibabas IPO, which could come as soon as Sept. 19, could raise more than $21 billion and claim Facebook Incs title of biggest tech IPO. Some analysts say large swaths of the market, especially biotechnology stocks, are frothy. Roughly one-third of the 188 stocks that debuted this year are selling below their IPO price.