Migrate the old style delayed_job delivery to ActiveJob delivery

[oveits]

In the moment, I am running two different approaches for delivering background jobs:

1. provision, delete/de-provision and read are performed via old style Provisioning.deliver method, which directly calls delayed_jobs.
2. synchronize is performed via new style GeneralJob.perform_later(...) method. The Provisioning model is used only for persistently saving the job to the database for later reference. Provisioning's deliver method is not called.

I need to find a one method fits all solution. Two possibilities:

A) Migrate old style to new style
B) change new style: e.g. call GeneralJob.perform_later within the Provisioning.deliver method (might be the better choice? This is to be discussed).

TODO:

1. Find best solution between A) and B) above.
2. Work on GeneralJob+Provisioning model cleaning topics like follows:

• recording of the number of attempts in Provisioning model
• link to delayed_job to be replaced by link to GeneralJob in Provisioning model.

The change is non-functional only with no impact on the service, so the prio could be set to low. However, it needs to be done in order to keep the code maintenable. Therefore, I raise it to normal prio.