Make sure that we always select the V2 version of the RequestResponseProtocol, when possible

[acerone85]

Context

We have two version of he protocol /fuel/req_res/0.0.1 (can return empty response in case of errors) and /fuel/req_res/0.0.2 (returns error codes). When a peer is dialled, one of these two protocols will be agreed for communication. However, the specification of RequestResponse in libp2p-rs does not mention how this is selected.

Suggested solution

One way to solve the problem is to allow /fuel/req_res/0.0.1 to be exchanged only for inbound or outbound connections.
Tradeoffs are discussed below:

1. If a peer P allows /fuel/req_res/0.0.1 only for inbound connections, then all nodes can safely dial P. However, P can only dial peers that support /fuel/req_res/0.0.2. If the majority of the network did not upgrade to use /fuel/req_res/0.0.2, then P could struggle to establish outbound connections, and will need to downgrade their node version.

2. If a peer P allows /fuel/req_res/0.0.1 only for outbound connections, then P can safely dial both nodes that support either /fuel/req_res/0.0.1 or /fuel/req_res/0.0.2, as well as nodes that support only /fuel/req_res/0.0.1. On the other hand, peers that support only /fuel/req_res/0.0.1 would not be able to dial P. If the majority of the network upgrades, nodes supporting only /fuel/req_res/0.0.1 could struggle to establish outbound connections, and will need to upgrade their node version.

I am listing both alternatives, but I believe that 2. is probably the best because it incentivises nodes to upgrade the node version.

Acceptance criteria

The P2P request response behaviour is updated to allow /fuel/req_res/0.0.1 either only for inbound or outbound connections.