Enable auto commit

This allows for delaying commits to the index if the commit is not forced.
This should reduce the number of commits, and immediately frees the
client, so that the job queue delays should disappear. This will of course
only happen if clients do not explicitely specify that the change should
be committed immediately.

Commits are made at least every 5,000 milliseconds when there are changes
to be made to the index, or when there are changes to 10,000 or more
documents.

Bug: 48164
Change-Id: Ie230f2e40e97fa1fb00f056d4631e64cbcbf9eae
Merge "Enable auto commit" into production