Add Baggage Support

[cicoyle]

The Dapr runtime has recently added support for baggage propagation. Here is the docs PR for reference as well. Baggage is a mechanism to propagate key-value pairs across service boundaries, which is useful for passing contextual information through distributed traces.

We should add a new function that users can use to add baggage propagation support, working for both gRPC and HTTP. This would enable users to provide baggage without having to import OpenTelemetry themselves.

consumer code example

We should have tests for both gRPC + HTTP for this functionality.

RELEASE NOTE: ADD Baggage Support

[WhitWaldo]

Just putting some notes here following an enlightening discussion with @x0n on Discord:

• Baggage differs from tracing in that it is captured with all requests and not potentially sampled
• Baggage is only well defined for HTTP and not for other functionality like messaging (e.g. with pure .NET event hubs with tracing enabled, baggage would not survive the trip across the boundary, but tracing will)
• Review how AsyncLocal<T> works with asynchronous logic in that at any point along the request path, it's available

[WhitWaldo]

Removing from the 1.16 release board for now as it's still unclear what should happen in the .NET SDK to support this.

[WhitWaldo]

It looks as though this is going to be getting better support at the .NET runtime level itself. On the plus side, this hopefully means that .NET 10 (released later this year will get these changes) and we can just document how to use what's already in the runtime to make all this Just Work.

On the downside, we'll have to wait and see whether the changes get backported to .NET 8+ or not. It's possible that this will only benefit users on the newest .NET release and that it'll take 2ish years for everyone to make the switch.

Either way, no work needed on the Dapr SDK to support this. It's up to developers to install the OpenTelemetry package themselves (especially in the meantime since System.Diagnostics.DiagnosticSource isn't compatible) to get this support.

Huge thanks to @x0n (I forget their GitHub handle) for help in understanding all of this.