Text needs correction for Standard GSI in Enterprise Edition 7.0

Text * The supervisor process persists to disk all changes made to individual indexes. Each index gets a dedicated file* needs correction on page https://docs.couchbase.com/server/7.0/learn/services-and-indexes/services/index-service.html

In EE standard GSI stores multiple indexes in a given file on disk (instead of each index getting a dedicated file). Please see https://docs.google.com/presentation/d/1qyFCatlo7rFii14Qizdghy-Dnx0CfdkaUlaUm2QVnZI/edit?ts=6019f681#slide=id.gbb19cae8aa_1_0 for more details on what changed underneath in 7.0/Cheshire-Cat.