Generate Telemetry doc from code to make sure it's always up to date

[RodgeFu]

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as title.

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[timotheeguerin]

I think this would be the job of a typespec telemetry library, we shouldn't go try to generate from the typescript code.
We could do a basic emitter that generate both the TS types and markdown doc that isn't published for now

import "@typespec/telemetry";

model Foo is Telemetry.Event {   
   action: string;  
   @Telemetry.hash  
   data: string;
}