Identify/Advertise Plugins used by peers

[DougAnderson444]

Associated with #1, there needs to be a consistent ways for peers to identify the plugins they are using. Couple of options:

1. Use the identify protocol system
2. Use the CID of the interface or code itself

There seems to be some challenges and differences with 1) here and here which make it not as straightforward as it might seem. Also we would have to verify that a "layer 2" protocol can interoperate at the "identify" layer. In other words, Plugins operate as Apps on Pubsub messages, like Ping operates on Request Response. If I have a chat program running on Pubsub, can I advertize it as libp2p/plugin/postr/1.0.0?

But for 2) we would have to determine where to advertise the CID, which is nicely taken care of at 1)

[DougAnderson444]

3. Request-Response has a ProtocolName system as well

https://docs.rs/libp2p/latest/libp2p/request_response/codec/trait.ProtocolName.html

Example

use libp2p_core::ProtocolName;

enum MyProtocolName {
    Version1,
    Version2,
    Version3,
}

impl ProtocolName for MyProtocolName {
    fn protocol_name(&self) -> &[u8] {
        match *self {
            MyProtocolName::Version1 => b"/myproto/1.0",
            MyProtocolName::Version2 => b"/myproto/2.0",
            MyProtocolName::Version3 => b"/myproto/3.0",
        }
    }
}