gitlab mattermost service API does not set all values properly
Summary
When using the gitlab API to activate de mattermost service on a project, some values are not taken into account (like the merge request checkbox) I noticed also that some others are not taken into account (I did not test them all)
Steps to reproduce
curl -XPUT -v -k --header "Private-Token: MYPRIVATETOKEN" "https://mydomain-gitlab.edf.fr/api/v4/projects/4915/services/mattermost?webhook=http%3A%2F%2Fmymattermostdomain.fr%2Fhooks%2F9d5siiz9j3g63em838qtmapfih&merge_requests_events=true"
Here is the output
{"id":20275,"title":"Mattermost notifications","created_at":"2018-06-18T14:36:47.997Z","updated_at":"2018-06-20T11:43:52.397Z","active":true,"push_events":false,"issues_events":false,**"merge_requests_events":false,"**tag_push_events":false,"note_events":false,"pipeline_events":false,"job_events":false,"properties":{"webhook":"http://noev02n2.noe.edf.fr/hooks/9d5siiz9j3g63em838qtmapfih","username":"","notify_only_broken_pipelines":"0","notify_only_default_branch":"0","push_channel":"","issue_channel":"","confidential_issue_channel":"","merge_request_channel":"","note_channel":"","tag_push_channel":"","pipeline_channel":"","wiki_page_channel":""}}
Results of GitLab environment info
GitLab Community Edition 10.3.6 c9d2f74c