Discontinue prometheus crate?

[cijothomas]

Given more and more native support from Prometheus to ingest OTLP, wondering if we should keep publishing the prometheus crate?
https://prometheus.io/blog/2024/11/14/prometheus-3-0/#otlp-support

[cijothomas]

Related: #1551 and #2769

I'd vote to mark this crate as deprecated in the coming release, and remove it fully. We can bring it back, when we have the bandwidth to rewrite it using the official prometheus crate and also avoiding the protobuf dependency which seem to be unmaintained (https://github.com/stepancheg/rust-protobuf/?tab=readme-ov-file#help)

[cijothomas]

@open-telemetry/rust-maintainers Do you see any concerns with the above? Happy to discuss ideas, but we should not be shipping crates that cannot be easily maintained/patched due to dependencies on unmaintained (or less actively maintained) crates IMHO.

[lalitb]

There have been contributions from outside to keep it in-sync with the new OTel releases. We can also continue that as long as we just do the publish. But I am also good with removing it altogether if all agree.

[cijothomas]

Yes those changes were relatively minor ones to keep up with upstream. but changing the dependencies is much bigger in scope and I think it'd be possibly require rewriting from scratch, and will be breaking changes for end users too
#1551