Add context propagation guideline for SQL Server

[XSAM]

Part of open-telemetry/semantic-conventions#2162, copied from open-telemetry/semantic-conventions#2363, as the OTel spec may be the best place to host this guideline.

XSAM/otelsql#508 is the prototype to demonstrate how SET CONTEXT_INFO works. You can run the example on your local Docker environment.

Changes

It proposes a way to propagate the context for SQL Server.

cc @jsuereth @lmolkova

[XSAM]

Per the spec SIG meeting, we want to move this back to the semantic convention, where this is the place people would look first to implement instrumentation for third parties.

A similar doc like https://github.com/open-telemetry/opentelemetry-specification/blob/main/supplementary-guidelines/compatibility/aws.md should also be moved to the semantic convention.

Closing it.