Add ability to drop cluster label after dedupe

[tomwilkie]

A couple of users have asked for this; as we need a cluster label for deduping in the distributors, some people don't have this and adding it will break their graphs.

By "break their graphs", they will cause things like discontinuations in things like recording rules, which for LTS systems is undesirable.

@cstyan is this something we can make an option?

[bboreham]

we need a cluster label for deduping in the distributors

why is this?

[cstyan]

The cluster label is used to differentiate between HA Prometheus "pairs", the __replica__ label identifies each replica in the pair.

[nbellowe]

This is a similar ask to #1736

Any status updates?

[cstyan]

There's a PR open: #1726