Refs #15779 - make background processing unavailable for now (#4217)

The original PR got vetted in the packaging phase and including
foreman-task as dependency of Foreman was refused. We need to rethink
our approach for getting the foreman-tasks functionality available
inside the core and take less obtrusive approach by making the
transition in several steps, until the foreman core will get on
future-parity with foreman-tasks which would effectively mean tasks in
core.

To clean the tasks that were created while using the original changes,
you can run:

rake foreman_tasks:cleanup\
    TASK_SEARCH="label = Actions::Foreman::Report::Import
      OR label = Actions::Foreman::PuppetClass::Import"\
    VERBOSE=true

This reverts commits

eb371ca33dcdd7a4f71d3cda0cfcad701cd3ae7e,
     69c34cd691aea4c7f21613f3859ae92a5f403529,
     3a1cd1dbeb74c60a482d7c47fc290c185d7c707a,
     0cf8ea6780c24954ccbe2cc33ca02e1f6010ffed,
     1538b8d2addb12f04da36a2c34224cd821e77acc,
     33709ef2813d0128f64905c6597616f44abad28e.