Use theforeman-rubocop gem

We have inherited strictest.yml here, because this rules have NewCops
enable config. Also dropped Style/HashSyntax and Style/Documentation
from here because that was also included in the inherit file.

.github/workflows/main.yml

@@ -15,6 +15,8 @@ jobs:
   rubocop:
     name: Rubocop
     uses: theforeman/actions/.github/workflows/rubocop.yml@v0
+    with:
+      command: bundle exec rubocop --parallel --format github
 
   test_ruby:
     name: Ruby

.rubocop.yml

@@ -1,26 +1,18 @@
 inherit_from: .rubocop_todo.yml
 
-require:
-  - rubocop-performance
-
-AllCops:
-  NewCops: enable
+inherit_gem:
+  theforeman-rubocop:
+    - strictest.yml
 
 Layout/LineLength:
   Enabled: false
 
 Metrics:
   Enabled: false
 
-Style/HashSyntax:
-  EnforcedStyle: no_mixed_keys
-
 Style/SymbolArray:
   EnforcedStyle: brackets
 
-Style/Documentation:
-  Enabled: false
-
 Style/StringLiterals:
   Enabled: false