More advanced relabel rules/processor for metrics

[mattdurham]

Background

Relabel rules are very focused on a few key areas but they dont have a ton of flexibility. The new array.combine_maps allows joining on discovery. But imagine where you have Kube State Metrics metrics come in and want to associate additional metadata from discovery.k8s or something external.

Proposal

The ability to have fine grained control on incoming metrics and being able to drop/enrich/add based on an external dataset, maybe represented as list of maps or other datastructure. Something akin to ottl or loki.process.

[mattdurham]

Pinging @bentonam and @petewall to clarify, add context or point out what I mistyped :)