Delegate a discussion in a merge request into a new issue.
The discussion wil be marked as resolved and a system note will be
added linking to the newly created issue.
When a merge request can only be merged when all discussions are
resolved. This feature allows to easily delegate those discussions to a
new issue, while marking them as resolved in the merge request.
The user is presented with a new issue, prepared with mentions of all
unresolved discussions, including the first unresolved note of the
discussion, time and link to the note.
When the issue is created, the discussions in the merge request will get
a system note directing the user to the newly created issue.
1) Adds a DB migration for all services to toggle on push, issue, and merge events.
2) Upon an issue or merge request event, fire service hooks.
3) Slack service supports custom messages for each of these events. Other services
not supported at the moment.
4) Label merge request hooks with their corresponding actions.
When a webhook for issues is triggered, it should also return the
resource URL, and the action that was performed (ie: Was it reopened,
updated, opened or closed)
