FEATURE: Optionally skip using full_name when suggesting usernames (#16592)

This commit introduces a new site setting: `use_name_for_username_suggestions` (default true)

Admins can disable it if they want to stop using Name values when generating usernames for users. This can be useful if you want to keep real names private-by-default or, when used in conjunction with the `use_email_for_username_and_name_suggestions` setting, you would prefer to use email-based username suggestions.

app/models/discourse_connect.rb

@@ -373,7 +373,8 @@ class DiscourseConnect < DiscourseConnectBase
   end
 
   def resolve_username
-    suggester_input = [username, name]
+    suggester_input = [username]
+    suggester_input << name if SiteSetting.use_name_for_username_suggestions
     suggester_input << email if SiteSetting.use_email_for_username_and_name_suggestions
     UserNameSuggester.suggest(*suggester_input)
   end