Fixes #12599 - Add config groups related apipie doc

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...

fixes #18214 - accept `params` as AC::Parameters or Hash

In Rails 5, ActionController::Parameters no longer inherits from Hash
and so type checks for params.is_a?(Hash) now return false and should
accept either. (Rails commit 14a3bd5.)

Refs #17653 - fix typo in show_hidden_parameters and add tests

Refs #17653 - add show_hidden to apidoc

Fixes #17653 - Allow all parameters api to unhide values

Fixes #17894 - load needed dependent api param group

when rendering facet api param docs

Fixes #13775 - merge if data set is present

Fixes #17678 - APIdoc - URL desc add missing CR types

Fixes #17525 - Add a friendly error message to invalid dns_id