By passing commit data to this worker we remove the need for querying
the Git repository for every job. This in turn reduces the time spent
processing each job.

The migration included migrates jobs from the old format to the new
format. For this to work properly it requires downtime as otherwise
workers may start producing errors until they're using a newer version
of the worker code.

Sorting by created_at can lead to uncertainties if two records are
created at the same time.

Signed-off-by: Rémy Coutable <remy@rymai.me>