Docs: Added RethinkDB River to list of community plugins

Closes #8016
Docs: Update query-string-query.asciidoc

Update sample

Closes #8024
Docs: fix typo

Closes #8111
Docs: Typo: s/by/be/

Closes #8114
Improve amibiguous ES_HEAP_SIZE warning in deb init script

Closes #3554
More improvements to debug logging for upgrade test.
Remove unnecessary log level setting in upgrade test.
Fixing copy/paste mistake in SearchRequest.extraSource's exception message.