Feature request: Add reason for silencing the user to system message template

Hey guys

In some cases users complained that they were silenced without a reason.
After a test we realized that the reason text for silencing is not included in the message sent from the system account.

It would be great if the reason for silencing could be added to the default system_messages.silenced_by_staff.text_body_template text.

Reason: some of our users either did not receive email due to simply not checking their inbox or having used a one time trash mail that expired.