[1.x] Implement Support for Translatable Validation Attribute Errors (#4070)

* chore: add validation translations

* feat: implement ability to translate validation attributes

* chore: change translation key

* style: formatting

* perf: cache `getAttributeNames`

* perf: cache `getAttributeNames`

* chore

* style: formatting

Author: DavideIadeluca

locale/en.yml

@@ -69,3 +69,7 @@ flarum-suspend:
         You have been unsuspended. You can head back to the forum by clicking on the following link:
 
         {forum_url}
+
+  validation:
+    attributes:
+      suspendedUntil: suspended until