Prometheus: Support forthcoming UTF-8 metric and label names in Prometheus

[ywwg]

Why is this needed:

Prometheus will be adding support for UTF-8 in metric and label names, and Grafana will need updates to properly support the new syntax, for instance when validating queries and also in the Builder. The Prometheus issue is here: prometheus/prometheus#13095

What would you like to be added:

Per the forthcoming design doc, Grafana will need to support the updated language syntax. This is not finalized yet.

Who is this feature for?

This will be for Prometheus users who have metric names that don't comply with the previous character requirements.

[ywwg]

Proposal has been merged: https://github.com/prometheus/proposals/blob/main/proposals/2023-08-21-utf8.md

[yuri-rs]

@ywwg I can try to help with the Grafana part of the project

[ywwg]

Great, thank you. I believe most of the task for Grafana will be supporting the new syntax in the code and builder views. For the code view, it needs to correctly recognize the syntax as valid, and for the builder view, it will need to construct queries with the new syntax when necessary. I am not sure how the functionality should be enabled -- I believe the datasource plugin will have to know what version of backend it's talking to.