[DS10] Support SchemaUrl on ActivitySource & Meter

[CodeBlanch]

See: dotnet/runtime#113034

[martincostello]

Can you provide some more specifics here on what's required?

#6307 has the update to System.DiagnosticsSource v10 in it, but it's not clear to me what's required here.

Is it to expose a setting for the end-use to specify a schema URL, or is it that we should create a schema that's hosted somewhere, then update all the ActivitySource and Meter instances to specify the appropriate URL?

If it's the latter than I guess that's the meat of the issue and needs to most work, and populating it in the relevant places would be fairly trivial.

[Kielek]

I think that in scope of this issue, we should start exporting newly added fields.
It especially affects OTLP exporter, but it will be great to extend also Cosnole and other if there is a possibility/specification/semantic convention mentions how to achieve this.

As a follow up, we should add these properties at least to stable packages.