Create gitlab issues for uploaded karaokes to Karaoke Mugen

[odrling]

We should create issues to Karaoke Mugen when a karaoke is uploaded.

Some notes though, the files are shared publicly and licensed under CC-BY-SA 4.0.
In the past that was implicitly acknowledged by just uploading to our database to which Mugen maintainers had access but it was technically a mistake to not explicitly mention it in some way.

We still want to encourage to share most of our karaokes to Mugen, but there should be an obvious way to opt out, either for a particular karaoke that should not be shared (this has already happened in the past), or for an user that would just not want to share his creations with Mugen for any reason.

[odrling]

partly done, missing the CC license and opt-out bits