Fix connect concurrency, can cause connection nodes to close
Looking at the connect code, if 2 threads at the same time try and connect to a node, and both enter sequentially the connectLock code block, the second one would try and put the connection in the map, and close the replaced channels, which will cause the existing connection to close as well (since it removes the node from the connectedNodes map)
To fix this, simply make sure we properly check the existence of the connection within the connectionLock block, so there won't be concurrent connections going on.
While doing this, also went over all the mutation code that handles disconnections, and made sure they are properly done only within a connection lock.
closes #6964
Unicast discovery: only disconnect from temporary connected nodes
In unicast discovery, we try to reuse existing discovery nodes based on the node address they have. If we find an existing node based on its address, and for some reason its not connected, don't add it to the list of nodes to disconnect from, as that (full) connection is useful down the road
closes #6966
[TEST] Add simple sort assertions for bwc tests

Today we only do count searches to ensure sane results are returned
after upgrading etc. This change adds sorting to the picture asserting
on simple numeric sorting that uses field data etc. after upgrading.

Relates to #6967
PhraseSuggester: Collate option should allow returning phrases with no matching docs

A new option `prune` has been added to allow users to control phrase suggestion pruning when `collate`
is set. If the new option is set, the phrase suggestion option will contain a boolean `collate_match`
indicating whether the respective result had hits in collation.

CLoses #6927