Weaver live check test util

[lmolkova]

Description

Adds WeaverLiveCheck helper that allows to validate instrumentation output against otel semconv.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[xrmx]

Love this, thanks a lot!

[xrmx]

Wondering if we can provide an helper that returns the report if one don't want to write policies for tests. I understand policies are natural for weaver but in tests I think plain assertions looks more natural. Also since policies works from the filesystem it may be a bit complicated to only match against a subset of the policies contained in a directory.
IOW providing an end method that will always return a report (and exit_code?) that can be called there as well.

[lmolkova]

Good point, I've done this:

1. you can call report = check.end() and it won't raise. You can explore report (which contains a list of violations and also full weaver report as dict from json) - party on

        with WeaverLiveCheck() as weaver:
            # ... configure provider, emit telemetry ...
            provider.force_flush()
            report = weaver.end()

        seen_metrics = report["statistics"]["seen_registry_metrics"]
        self.assertEqual(seen_metrics.get("test.metric"), 1)

2. you can call report = check.end_and_check() and it'd raise LiveCheckError (extends AssertionError) if any violations are found. You still get full report as a property on the error if you want to assert on more

        with WeaverLiveCheck() as weaver:
            # ... configure provider, emit telemetry ...
            provider.force_flush()

            with self.assertRaises(LiveCheckError) as cm:
                weaver.end_and_check()

        seen_metrics = cm.exception.report["statistics"]["seen_registry_metrics"]
        self.assertEqual(seen_metrics.get("test.metric"), 1)

wdyt?