Add schema URL support

[tarekgh]

https://github.com/open-telemetry/opentelemetry-specification/tree/main/specification/schemas

Telemetry sources such as instrumented applications and consumers of telemetry such as observability backends sometimes make implicit assumptions about the emitted telemetry. They assume that the telemetry will contain certain attributes or otherwise have a certain shape and composition of data. Essentially there is a coupling between 3 parties: OpenTelemetry semantic conventions, telemetry sources and telemetry consumers. The coupling complicates the independent evolution of these 3 parties. The 3 parties should be able to evolve independently over time and Telemetry Schemas are central to how we make this possible.

Proposal

namespace System.Diagnostics
{
    public sealed class ActivitySource : IDisposable
    {
        public ActivitySource(string name, string? version = "") { ... }
+       public ActivitySource(string name, string? version, string? telemetrySchemaUrl) { ... }
+       public string? TelemetrySchemaUrl { get; }
    }
}

namespace System.Diagnostics.Metrics
{
    public class Meter : IDisposable
    {
        public Meter(string name) { }
        public Meter(string name, string? version)  { }
+       public Meter(string name, string? version, string? telemetrySchemaUrl)  { }
+       public string? TelemetrySchemaUrl { get; }
    }
}

Usage

    private static ActivitySource s_source = new ActivitySource("MyLibrary.MyFeature", "2.0", "https://opentelemetry.io/schemas/1.2.0");
    private static Meter s_meter = new Meter("MyLibrary.MyFeature", "2.0", "https://opentelemetry.io/schemas/1.2.0");

Tagging subscribers to this area: @dotnet/area-system-diagnostics-activity
See info in area-owners.md if you want to be subscribed.

Issue Details

---

open-telemetry/opentelemetry-dotnet#2417
https://github.com/open-telemetry/opentelemetry-specification/pull/1666/files

Author:	tarekgh
Assignees:	-
Labels:	feature request, area-System.Diagnostics.Activity
Milestone:	7.0.0

[tarekgh]

We are going to wait for finalizing the semantic convention discussion on OpenTelemetry side to know if there will be any effect on this current proposal. We expect to have the feedback by the end of March or early April.

CC @cijothomas @reyang @denisivan0v

[CodeBlanch]

Just looking at open-telemetry/opentelemetry-dotnet#3445. There are cases where instrumentation does not own the ActivitySource being used (ex AspNetCore, HttpClient). In those cases it might be helpful to make some of this data settable?

namespace System.Diagnostics
{
    public sealed class ActivitySource : IDisposable
    {
        public ActivitySource(string name, string? version = "") { ... }
+       public ActivitySource(string name, string? version, string? telemetrySchemaUrl) { ... }
        public string? Version { 
          get;
+         set;
        }
+       public string? TelemetrySchemaUrl { get; set; }
    }
}

That would allow (for example) OpenTelemetry instrumentation augmenting the sources to pass along its version + schema url for the schema being augmented.

Breaks if users have multiple augmenting libraries/schemas, but may not be a concern?

[danelson]

@tarekgh I am curious if this was revisited at all with some of the changes made for .NET 8 (e.g. https://github.com/lmolkova/semantic-conventions/blob/dotnet8-metrics/docs/dotnet/dotnet-http-metrics.md). There was a comment that mentioned staying compatible with OTel but I am a bit concerned that this will be hard for consumers to manage if there are additional changes without the existence of schema URL. Do you have any idea when I might be able to expect this change?

Speaking from someone whose organization sticks to mainly LTS releases, if this does not make .NET 8 then it becomes hard to manage across various language SDKs.

[tarekgh]

@danelson the semantic convention discussion came very late in the 8.0 after passing the point of adding a new API. This is something we can consider for our next release.

CC @reyang @noahfalk @CodeBlanch