Add setting to disable the anti-spam (#11296)

* Add environment variable to disable the anti-spam

* Move antispam setting to admin settings

* Fix typo

* antispam → spam_check

app/lib/spam_check.rb

@@ -14,7 +14,7 @@ class SpamCheck
   end
 
   def skip?
-    already_flagged? || trusted? || no_unsolicited_mentions? || solicited_reply?
+    disabled? || already_flagged? || trusted? || no_unsolicited_mentions? || solicited_reply?
   end
 
   def spam?
@@ -80,6 +80,10 @@ class SpamCheck
 
   private
 
+  def disabled?
+    !Setting.spam_check_enabled
+  end
+
   def remove_mentions(text)
     return text.gsub(Account::MENTION_RE, '') if @status.local?