* [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