Add support for posting notices as GitLab Issues

[jhuntwork]

Slack is great, but we prefer track events like this as issues to follow up on via a private GitLab server. If the right combination of GITLAB env variables are set, this will create a new issue for each new release.

Since this adds a new destination type, and it's uncertain if that is desirable, for now there is bit of code duplication just to demonstrate the feature.

Thanks for considering!