Print the number of conflicts in Slack

When creating an upstream merge request, and posting it to Slack, also inform the number of conflicts exist in that merge request.

For regular merge requests:

Created a new merge request https://gitlab.example.com/grp/prj/merge_requests/1234|grp/prj!1234

For merge request without conflicts:

Created a new merge request https://gitlab.example.com/grp/prj/merge_requests/1234|grp/prj!1234 with no conflicts! 🎉

For merge request with conflicts:

Created a new merge request https://gitlab.example.com/grp/prj/merge_requests/1234|grp/prj!1234 with 3 conflicts! ⚠