related issue: #3306
Note: this PR just remove the es_scan_node_test.cpp which is useless
For the moment, just add a simple explain syntax for EsTable without translating the native predicates to ES queryDSL which is better to finished with moving the predicate translating from Doris BE to Doris FE, the whole work is still WIP.
NOTE: This patch would modify all Backend's data.
And this will cause a very long time to restart be.
So if you want to interferer your product environment,
you should upgrade backend one by one.
1. Refactoring be is to clarify the structure the codes.
2. Use unique id to indicate a rowset.
Nameing rowset with tablet_id and version will lead to
many conflicts among compaction, clone, restore.
3. Extract an rowset interface to encapsulate rowsets
with different format.
