fix: Check uploaded file size in widget and dashboard (#1975)

* File size check logic in widget

* set maxium file size

* update locale texts

* file size check in dashboard

* dynamincally set file size limit error message

* code climate review fixes

* add alert mixin

* move attahcment bus event to constants

* Move file size check logic to helper

* add specs for file size limit check helper

* changes as per review

app/javascript/widget/i18n/locale/en.json

@@ -48,5 +48,6 @@
         "ERROR": "Message too short"
       }
     }
-  }
+  },
+  "FILE_SIZE_LIMIT": "File exceeds the {MAXIMUM_FILE_UPLOAD_SIZE} attachment limit"
 }