Core: remove built-in support for Lucene's experimental codecs

Lucene's experimental codecs (from the codecs module) do not provide
backwards compatibility and are free to change from release to
release.  When they do change, they typically cannot in general read
older indices and the resulting exceptions look like index corruption.
So, we are removing built-in support for them to prevent applications
from choosing one and then seeing strange exceptions on upgrade.

Closes #7566

Closes #7604
Doc: Fixes node client section name on Java API Doc

Closes #7539
[SEARCH] Execute search reduce phase on the search threadpool

Reduce Phases can be expensive and some of them like the aggregations
reduce phase might even execute a one-off call via an internal client
that might cause a deadlock due to execution on the network thread
that is needed to handle the one-off call. This commit dispatches
the reduce phase to the search threadpool to ensure we don't wait
for the current thread to be available.

Closes #7623
[STORE] Write Snapshots directly to the blobstore stream

Today we serialize the snashot metadata to a byte array and then copy
the byte array to a stream. Instead this commit moves the serialization
directly to the target stream without the intermediate representation.