Remote write v2 support

[ipe4647]

Hi!

This implementation only supports v1. I have an issue where opentelemetry collector prometheusreceiver is only supporting v2 and thus i can't send metrics with this package.

Support for v2 would be much appreciated.

Docs: https://prometheus.io/docs/specs/remote_write_spec_2_0/#io-prometheus-write-v2-request

[huksley]

Yes, would be nice to support. I am really busy now so might take a while. Would you be open to help by creating a pull request?

[ipe4647]

@huksley I can provide AI generated code for you to validate. I tested it with a local prometheus instance.