fix bulk args validation

detected type missmatch if one value was null
sync changelog with 0.42 branch
add request handling for QueryShardRequest/Response
change ESSearchTask to use QueryThenFetch using QueryShardRequests
fix test flakiness
generate lucene Sort from symbols
support missing values in new InputFieldComparator
add missing ensureGreen in tests and don't route to initializing shards
disallow order by on unknown columns
rename SearchNode/SearchTask; remove sort support from ESQueryBuilder