Create prototypes to validate the proposed semantic conventions for messaging

[pyohannes]

The messaging workgroup has already merged and is still working on several changes to the existing semantic conventions, the most important one being a proposal for span structures for messaging scenarios (open-telemetry/oteps#220).

In order to ground and illustrate the proposed changes, prototypes for several messaging scenarios utilizing those proposed changes need to be created. This is a pre-requisite for declaring stability on any messaging related conventions.

[pyohannes]

@lmolkova analyzed existing Azure SDK messaging instrumentation and its compatibility with the proposed span structure OTEP: open-telemetry/oteps#220 (comment)

[pyohannes]

For stability, we will require prototypes for both traces and also metrics.

[pyohannes]

Here's a PR implementing the span semantic conventions for RabbitMQ in .NET: rabbitmq/rabbitmq-dotnet-client#1261

[pyohannes]

Here's one with Kafka instrumentation in the .NET auto-instrumentation project: open-telemetry/opentelemetry-dotnet-instrumentation#3055

[pyohannes]

As discussed on today's workgroup meeting, here's a list with prototypes for messaging semantic conventions which are either currently available or planned.

Language	Product	Traces	Metrics
.NET	Rabbit MQ client	✔️
.NET	Kafka auto-instrumentation	✔️
.NET	Kafka instrumentation library	✔️	✔️ (partly)
Java	Azure SDKs	✔️	✔️
.NET	Azure SDKs	✔️	planned early 2024
Python	Azure SDKs	✔️
JS	Azure SDKs	✔️
Go	Google Pub/Sub	✔️	planned late 2024
C++	Google Pub/Sub	✔️
JS	Google Pub/Sub	✔️	planned late 2024
Java	OpenTelemetry instrumentation	planned	planned
Python	OpenTelemetry instrumentation	planned	planned
.NET	MassTransit	planned	planned
Go	Kafka (Sarama)	✔️	planned