Allow departments to be enabled/disabled by users

Over in rubocop/rubocop#9752 we figured out
that the reason end-users can't enable/disable Cookstyle departments is
because `Enabled` isn't in the config and thus [can't be
overridden](rubocop/rubocop#9752 (comment)).

This change will allow a user to not only do the obvious:

```yaml
Chef/Correctness:
  Enabled: false
```

But more interestingly do something like this:

```yaml
AllCops:
  DisabledByDefault: true

Chef/Correctness:
  Enabled: true
```

CC @jonas054

config/cookstyle.yml

@@ -12,6 +12,7 @@ AllCops:
 ###############################
 
 Chef/Style:
+  Enabled: true
   StyleGuideBaseURL: https://docs.chef.io/workstation/cookstyle/
 
 Chef/Style/AttributeKeys:
@@ -156,6 +157,7 @@ Chef/Style/IncludeRecipeWithParentheses:
 ###############################
 
 Chef/Correctness:
+  Enabled: true
   StyleGuideBaseURL: https://docs.chef.io/workstation/cookstyle/
 
 Chef/Correctness/ServiceResource:
@@ -529,6 +531,7 @@ Chef/Correctness/InvalidNotificationResource:
 ###############################
 
 Chef/Sharing:
+  Enabled: true
   StyleGuideBaseURL: https://docs.chef.io/workstation/cookstyle/
 
 Chef/Sharing/InsecureCookbookURL:
@@ -597,6 +600,7 @@ Chef/Sharing/IncludeResourceExamples:
 ###############################
 
 Chef/Deprecations:
+  Enabled: true
   StyleGuideBaseURL: https://docs.chef.io/workstation/cookstyle/
 
 Chef/Deprecations/NodeDeepFetch:
@@ -1301,6 +1305,7 @@ Chef/Deprecations/DependsOnOmnibusUpdaterCookbook:
 ###############################
 
 Chef/Modernize:
+  Enabled: true
   StyleGuideBaseURL: https://docs.chef.io/workstation/cookstyle/
 
 Chef/Modernize/LegacyBerksfileSource:
@@ -1973,6 +1978,7 @@ Chef/Modernize/DeclareActionClass:
 ###############################
 
 Chef/RedundantCode:
+  Enabled: true
   StyleGuideBaseURL: https://docs.chef.io/workstation/cookstyle/
 
 Chef/RedundantCode/ConflictsMetadata:
@@ -2195,6 +2201,7 @@ Chef/RedundantCode/DoubleCompileTime:
 ###############################
 
 Chef/Effortless:
+  Enabled: true
   StyleGuideBaseURL: https://docs.chef.io/workstation/cookstyle/
 
 Chef/Effortless/CookbookUsesSearch: