Add a basic gitlab issue template
This makes the Bug template available in the new issues form. Ideally a majority of users will select this template and then realize that they're in the wrong repo.
Making this a default is a feature of the enterprise gitlab version only, see https://docs.gitlab.com/ce/user/project/description_templates.html#overview
Note: I filed this from my master branch so you can easily check how it works by starting a new issue in https://gitlab.freedesktop.org/whot/wayland/-/issues