Provide anonymised user id for acoustid/mbid pair submissions

[ijabz]

It would aid in finding bad data feeds if we we could group together submissions from particular users, there is no requirement to know who the user is just would be useful to know all if a group of submissions is from particular user in order to detect bad submissions

Could also be used to protect against any user intentenionally sabotaging data, see discussion https://community.metabrainz.org/t/detecting-bad-actors-acoustid-submission-group