[Feature]: trace propogation over http using reqwest as the client

[Shahab96]

Related Problems?

The HeaderInjector trait provided here does not satisfy the type for reqwest's HeaderMap. This means that consumers using reqwest for making http requests will have to inject the traceparent header manually.

Describe the solution you'd like:

I'd like the trait to be implemented for reqwest::HeaderMap as well as (if possible) an implementation for reqwest's client builder.

Considered Alternatives

I've considered copying the manual instrumentation into my own code.

Additional Context

I'd be more than happy to make the changes required for this!