Add UUID or hash of `external_url` in usage ping to disambiguate multiple instances
Right now there is some confusion as a few customers upload the same license to multiple instances, causing usage ping data to look a little odd.
We should add a UUID for each host or a hash the external_url
to help make it easier to sort these out.
/cc: @rdavila, @rymai, @DouweM, @victorwu
MR: https://dev.gitlab.org/gitlab/version-gitlab-com/merge_requests/47