Add account migration UI (#11846)

Fix #10736

- Change data export to be available for non-functional accounts
- Change non-functional accounts to include redirecting accounts

app/models/remote_follow.rb

@@ -49,7 +49,7 @@ class RemoteFollow
   end
 
   def fetch_template!
-    return missing_resource if acct.blank?
+    return missing_resource_error if acct.blank?
 
     _, domain = acct.split('@')