Revise queryTmpSpaceDir & queryTmpSpaceSize descriptions.

Here:

https://docs.couchbase.com/server/current/settings/query-settings.html

(and elsewhere):

Revise "queryTmpSpaceDir":

< "The path to which the indexer writes temporary backfill files, to store any transient data during query processing."

> "The path to which the indexer writes temporary backfill files and the Query service writes spill files, to store any transient data during query processing."

Revise "queryTmpSpaceSize":

< "The maximum size of temporary backfill files (MB)"

> "In MiB, the maximum size of temporary backfill files for each indexer and the maximum size of temporary files for spilled sorting and other operations.  In a cluster with both secondary indexing and full text search, the limit for disk space use is three times this setting."