Enabling Mattermost slash commands raises error logs about notifications.log not being accessible
On enabling Mattermost Slash Commands integration, Mattermost logs show the following
$ gitlab-ctl tail mattermost
2020-03-19_15:58:03.32147 {"level":"warn","ts":1584633483.3211272,"caller":"app/notification.go:261","msg":"Notification not sent","logSource":"notifications","ackId":"","type":"message","userId":"opoahro6k3yo9j34odnwmkj3yw","postId":"531df6tgfigaun7ckaingyxsjw","status":"Not Sent due to preferences"}
2020-03-19_15:58:03.32164 2020-03-19 15:58:03.321618328 +0000 UTC m=+238.520831654 write error: can't open new logfile: open notifications.log: permission denied
2020-03-19_15:58:47.86864 {"level":"warn","ts":1584633527.8685524,"caller":"app/notification.go:261","msg":"Notification not sent","logSource":"notifications","ackId":"","type":"message","userId":"opoahro6k3yo9j34odnwmkj3yw","postId":"j8uem9ibcffkmgtcyn9hdo7xgw","status":"Not Sent due to preferences"}
2020-03-19_15:58:47.86868 2020-03-19 15:58:47.86863812 +0000 UTC m=+283.067851417 write error: can't open new logfile: open notifications.log: permission denied