add CommTagAttribute for metric code generator

[BowenYang666]

Support common tag and value for the same group of metrics

[CommonTag("Category", "Http")]
[CommonTag("MetricVersion", "v1")]
 static partial class Metric
 {
    [Counter("RequestName", "RequestStatusCode")]
    static partial RequestCounter CreateRequestCounter(Meter meter);
}

Microsoft Reviewers: Open in CodeFlow

[BowenYang666]

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[dariusclay]

This seems like a cool idea. Did you write up an API proposal for this? Since it's a new feature we might want to discuss it there, so that we don't end up having to change things later.

[dariusclay]

Should use the well-defined experiment IDs

Suggested change

	[Experimental("EXPERIMENTAL_COMMON_TAG_ATTRIBUTE")]
	[Experimental(diagnosticId: DiagnosticIds.Experiments.Telemetry, UrlFormat = DiagnosticIds.UrlFormat)]

[BowenYang666]

This seems like a cool idea. Did you write up an API proposal for this? Since it's a new feature we might want to discuss it there, so that we don't end up having to change things later.

Thanks Darius. I have created a new feature proposal here:
#6259