Fixes #19700 - update rubocop rules

The following changes have been made:

- Performance/RedundantMerge:
changes lines such as:
```not_found_message.merge! :message => options```
to:
```not_found_message[:message] = options```

- converts str.match() to str =~ ()...

fixes #18982 - replace AC::Params#each using one-arg block

ActionController::Parameters#each works differently in Rails 5.0: it no
longer yields an array of [key, value] entries for hashes, only the
key when given a block with arity of one. This method now iterates over...

Fixes #18582 - add missing id params to taxonomy apidoc

Fixes #12294 - Update existing params using API

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...

Refs #17653 - fix typo in show_hidden_parameters and add tests

Refs #17653 - add show_hidden to apidoc

Fixes #6502 - List ignored classes and environments on import

When importing environments and classes from puppet, ignored
environments and classes defined in ignored_environments.yml
aren't aparent.

This will add them to the list to import as ignored and...

Fixes #15779 - make background processing available

Fixes #17343 - set deep munge config off

deep_munge was introduced as a solution to keep
Rails secure by default which results in
'empty array becomes nil in params'.
Thats why, set deep_munge config off in application.rb.
Also, added changes which will cast param argument to string...