Stabilize messaging semantic conventions for tracing

[pyohannes]

This OTEP aims to describe the necessary changes for bringing the existing semantic conventions for messaging from the current experimental to a stable state.

It is based on OTEP 0173, which defines basic terms and describes messaging scenarios that should be supported by the semantic conventions.

NOTE: This is an early draft document. It captures results of discussions currently going on in the messaging workgroup.

[Oberon00]

@brunobat https://github.com/open-telemetry/oteps/pull/192#pullrequestreview-1111964150

Please check https://github.com/open-telemetry/oteps/pull/207 because the propagation will soon might have

#207 should not be relevant to this PR at all. It does not change anything regarding propagation.

[pyohannes]

The messaging workgroup was capturing findings and results of discussions in this draft PR. As this draft PR got very big and it got hard to keep track of discussions going on in comments, the workgroup decided to close this PR and work on different artifacts:

• Proposed changes for context propagation are already merged into the specification (https://github.com/open-telemetry/opentelemetry-specification/pull/2750).
• Proposed changes for trace and span structure are captured in #220.
• Proposed changes to attributes are covered in https://github.com/open-telemetry/opentelemetry-specification/pull/2763.