Default GSI client disk quota for backfill should be set lower

I just had a long running query cause my disk to fill up because of the indexer scan backlog (I presume?), causing the node to crash and restart

I noticed that the indexer temp directory is set to /opt/couchbase/var/lib/couchbase/temp by default with a quote of 5gb which means it risks filling up the root partition.

I think we need to do a few things to improve this:

1 - The default location should be with either the index directory so that when that is changed to a larger volume, this data goes along with it

2 - The quota should be set to 10% of its disk partition size or 5GB, whichever is smaller

3 - We need to provide better metrics to the user about how and where this space is being taken up.