Azure Service Bus: Clarify metadata

[gregkalapos]

So far, no agent had distributed tracing and span link support for Azure Service Bus. .NET implemented it recently and it uses the diagnostic-id application property - as suggested in the spec.

For clarity and better compatibility across agents, this PR removes the word "possibly" - so diagnostic-id should be the default metadata for trace context propagation in case of Azure Service Bus.

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#### Build stats * Start Time: 2022-08-15T04:57:00.804+0000 * Duration: 3 min 3 sec