Add support for pushint oltp metrics

[tiny-pangolin]

Issue Details

I would like the ability to have metrics pushed in otel format so I can resuse dashboards and alerting rules between caddy and other reverse proxies that follow otel semantic conventions

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[francislavoie]

That's already supported https://caddyserver.com/docs/metrics#caddys-metrics unless I misunderstand

[tiny-pangolin]

Those metrics are exposed in Prometheus format which is what I'm using now, but it would nice if caddy could be configured to push the metrics using the otlp protocol and follow the semantic conventions for http requests

[francislavoie]

Okay, seems related to #5743. Duplicate?

As I wrote there, most of Caddy's core maintainers don't use tracing or metrics ourselves, so we need to lean on the community to contribute improvements.