Increase default queue concurrency
Increase default queue concurrency

Following a test of publishing-api losing connectivity
in staging, we found that the rate at which search-api
can process jobs in the default queue was too slow.

Increasing it from 8 to 16 to see if we can get search-api
to process jobs faster without impacting performance of
search queries.

alphagov/rummager,alphagov/rummager