multi-tenancy support for Cortex and Mimir with solution similar to Loki Exporter

[salvovitale]

Hello everyone,

I wanted to start a discussion about multi-tenancy support for a metrics exporter in the OpenTelemetry collector. Specifically, I'm interested in exploring whether it's possible to implement a similar approach to the already available Loki exporter, which allows the tenantID to be injected as a Resource Attribute of ResourceMetrics or as an Attribute of NumberedDataPoint.

If someone has already started working on a similar contribution, I'd love to offer my help. Alternatively, if there isn't an existing effort already in place, I'd like to explore creating a new exporter myself.

I came across this issue (#7945), where someone attempted to extend the prometheusremotewriteporter, but their contribution was never merged. Additionally, that approach is limited to having the tenantID only as prometheus metric label, which when converted to Otel format only translates to an Attribute in the NumberedDataPoint.

I'd appreciate any thoughts or insights on this topic, and if anyone has any suggestions on how to approach this problem, I'd love to hear them. Thank you!

[salvovitale]

@kovrus @frzifus