* [Feature] Officially support ElasticSearch 7 as backend storage

* Extract bootstrap module to be shared by multiple starters

* Add missing configuration file and distinguish different version in test

* Update known-oap-backend-dependencies-es7.txt

Update the dependency lib

* Fix missing adaptation to ElasticSearch 7

* Rename ElasticSearch 7 specific class with Es7 infix

* Fix miss-adapted ElasticSearch DAO API

* Add ES7 specific configuration and polish documentations

* Polish documentations

* Polish documentations