Implement sending requests of request/response protocols in network bridge

[haikoschol]

Issue summary

The code that implements the parachain protocol uses an abstraction for communicating with the network via overseer messages called the network bridge. So far, it only supports gossip (aka notification) protocols. Some subsystems also need to use request/response protocols where messages are sent to a specific peer, which then sends a response back. Specifically sending out requests of certain request/response protocols and receiving the response from the peer.

Implementation details

There is a TODO in NetworkBridgeSender.processMessage() for adding the SendRequests message type. This type probably needs to include the network protocol to use, the peer to send the request to and the payload of the request.
The second part of the implementation covers routing the response back to the origin of the request via the overseer.

Other information and links

• SendRequests in Parity node implementation

• map of protocol names in Parity node

• Implement receiving requests of request/response protocols in parachain subsystems #4453 covers the other direction: subscribing to requests for a certain protocol and sending back responses.

Acceptance criteria

• New code is 60% covered with unit tests

[haikoschol]

While working on this I found out that collator-protocol already uses request/response network protocols. The implementation does not use SendRequests messages to network bridge though. Instead the subsystem depends on the network service directly and instantiates a RequestResponseProtocol through it.

[haikoschol]

implemented in #4475