Added mattermost config options that were introduced in version 3.4
Fixes: #1592 (closed)
Adds the mattermost config options additions from: https://docs.mattermost.com/administration/changelog.html#config-json
Fixes: #1592 (closed)
Adds the mattermost config options additions from: https://docs.mattermost.com/administration/changelog.html#config-json