[FEATURE REQ] EventHubs distributed tracing: span kind changes

[lmolkova]

Is your feature request related to a problem? Please describe.
Tracing visualization tools need to know when they are dealing with async messaging scenarios.

Describe the solution you'd like

EventHub spans kinds were not correct in the previous guidance. They should be changed to

• Message: 'producer' kind for OpenTelemtery (was 'internal'). OpenCensus does not support 'producer' - 'internal' should still be used there
• Send: 'client' kind (was 'producer')
• Processing: 'consumer' kind (was 'server'), OpenCensus should continue using 'server'

Note: As discussed offline, opencensus support may be dropped at this point.

This complies with OpenTelemetry semantics and helps backend tools understand they are dealing with async message processing and visualize it accordingly.

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