Bug 27783: Replace --job-type by --queue

Bug 27783: Replace --job-type by --queue

This patch adds a new column background_jobs.queue, which default to
'default'
By default, new jobs are enqueued into this default queue, and the
background job worker will subscribe to the default queue unless told
otherwise by the --job-queue option

The new job UpdateElasticIndex is automatically enqueued in another
queue named 'index'
So you can have 'default' worker with
    misc/background_jobs_worker.pl
and a dedicated indexing worker with
    misc/background_jobs_worker.pl --queue index

This is to address bug 27344 comment #15

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>