manage number of partitions of job-offers topic

[minh-adimian]

At the moment, users have to create a 'job-offers' topic and set the number of partitions themselves to avoid topic automatic creation. My proposition is to manage an ENV variable that store the number of partitions in this topic.

Users then can use kirby cli to set/change this value. On the event of change, a procedure will be run to update this topic's number of partitions. Furthermore, when starting supervisors, we can check this ENV variable so that one cannot start too many supervisors that exceed this value.