Detect name collisions around _bucket, _count, _sum, and the quantile label during registration

[beorn7]

With Once #222 is done, we can now then detect above mentioned collision during registration time.

See #108 for more details.

[jeffwidman]

This implies #222 is done, but confusingly that issue is not marked as close... is this still blocked by work that needs to happen in #222?

[beorn7]

Yeah, that's confusing indeed. I don't know what I thought when I wrote that. I'll try to improve the wording.

[beorn7]

I mostly assigned this to myself as a “default” because I used to be the maintainer of this repo. Therefore, I'm un-assigning this from myself no. New maintainers @bwplotka & @kakkoyun, please deal with this as you see fit.