hide join/leave messages in Team Edition
Admins can enable/disable join/leave messages in config console
This is planned at the user level here: https://mattermost.atlassian.net/browse/MM-11658
Setting this at the user level does not meet the request.
The request is specifically for admins to be able to control whether join/leave messages are displayed either universally or per channel (preferred). Asking each user to go to their settings and turn off these messages is unrealistic. As I understand it, these controls exist in the E10 version which means it is not unrealistic to expect it would be fairly straightforward to add this specific feature to the team edition.