Reject remote write request with wrong labels

[bwplotka]

We have an incident where users were not sending cluster IDs so the series was not unique across clusters. I think it would be useful for everyone if we would validate some of it on runtime? 🤔

E.g if you have _id label name in one of labels as per: https://rhobs-handbook.netlify.app/services/rhobs/#metric-label-restrictions