HTTP Post timeout - Optimize the good path in DID Comm communication

We need to restructure the code to optimize the good path when sending a DID Comm message via HTTP Post.

We have created an interface called Transport when a channel is open to receive/send DID Comm messages. As a way to uniform HTTP Posts and Websocket.

https://github.com/input-output-hk/atala-prism-mediator/blob/e032c3365f7b9ed0782bbd67a4f2809b40c18338/mediator/src/main/scala/io/iohk/atala/mediator/DIDCommRoutes.scala#L63-L71

We then pass this transport object to the underlying system for doing all the things necessary including problem reports.
Although, the way that we close the channel when he's there is no reply or problem to report is by a timeout.
This timeout should be removed but to do that we need to restructure the code, and put rules to close the Transport when there is no immediate need of it (in the case of HTTP Post)