Stabilize Telemetry Stability document

[pellared]

What are you trying to achieve?

https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/telemetry-stability.md marked as stable.

Additional context.

Having this document as experimental brings confusion if it must be adopted. E.g.

• Instrumentation.AspNetCore and Instrumentation.Http 1.8.1 have illegal breaking changes in the produced telemetry opentelemetry-dotnet#5541 (comment)
• Add schema URL support dotnet/runtime#63651 (comment)

It would be very good to have it stable given that we already have HTTP semantic conventions marked as stable.

CC @open-telemetry/semconv-http-approvers @open-telemetry/specs-semconv-approvers

[tigrannajaryan]

@jsuereth do you think this should be moved to semconv or stay in spec?

(@jack-berg will add this to the next spec meeting agenda).