Add support to track disk usage

[rishabhc32]

Description

Currently, there is no support for tracking disk usage. It will help to set up alerts where disk size grows beyond a set threshold.

[alexmojaki]

I think this would be a good feature request for the system metrics instrumentation in https://github.com/open-telemetry/opentelemetry-python-contrib. But this should work:

import psutil
import logfire
from opentelemetry.metrics import CallbackOptions, Observation

logfire.configure()


def disk_usage_callback(_options: CallbackOptions):
    usage = psutil.disk_usage("/")
    yield Observation(usage.percent / 100)


logfire.metric_gauge_callback("system.disk.utilization", [disk_usage_callback])

[Kludex]

Shall we, at least, document?