Trailers support in reqwest

[rgrandl]

We're using reqwest to send/receive HTTP requests.

However, reqwest doesn't allow propagating trailers which is needed for gRPC.

We would really appreciate if trailers support can be added to reqwest.

[seanmonstar]

Adding support is welcome. 🤓

[Lori-Shu]

this may need adding a trailers field in struct Request which is in http project,and some reconstruction in tower project . reqwest do storing the trailers map,validating,header adding,I think.

[seanmonstar]

No, hyper/http already support trailers on the body, and tower doesn't need to do anything. It's all work in reqwest to add support.

[Lori-Shu]

No, hyper/http already support trailers on the body, and tower doesn't need to do anything. It's all work in reqwest to add support.

oh,seems I have to dig deeper.