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:

ctx = client.WithBaggage(ctx, map[string]string{
    "user-id": "12345",
    "tenant": "acme",
})

client.InvokeMethod(ctx, ...)

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

[PrinsonF77]

Hey @cicoyle . I would like to take this up if it's still open and looking for contributions!