We use mattermost from Gitlab Community Edition (gitlab-ce-8.3.4-ce.0.el7.x86_64.rpm)
Last evening I wanted to setup a webhooks for my Team and gitlab-ci But I can’t set up my self or any other to be in Administrative role, as we use SSO with gitlab instance - which uses our LDAP (AD) directory.
Right now any user should be able to see Account Settings > Integrations > Incoming Webhooks once the webhooks are enabled by the System Administrator.
(Please note if you change settings via the Mattermost System Console instead of the gitlab.rb file, it is recommended you backup the Mattermost config.json file before updating or reconfiguring GitLab to avoid losing your settings).