OeX_ES-44: Update edx-search elasticsearch.
* removes redundant doc_types from the lms/cms, replaces courseware
index with doc_types to two indices
* code polishing
* Use a new config variable for ES7 deployment. (#2226)
Co-authored-by: Golub-Sergey <1.golub.sergey.1@gmail.com>
Co-authored-by: Diana Huang <diana.k.huang@gmail.com>