Implement a connection idle

[dariusc93]

New connections that are established without any activities would close almost immediately. Eg, if the node isnt subscribed to the same topic as another peer, or if dht is not performing queries, the connection may close right away after a connection is established. This is more observed when connecting to another peer over relay from actual use. While this isnt a problem, it might be better to implement a behaviour with a handler that keeps the initial connection alive for a specific amount of time (that is configurable) before allowing swarm to close the connection handler.

Note:

• This is a workaround until swarm: Introduce an idle_connection_timeout config option libp2p/rust-libp2p#4121 is resolved.
• This will deprecate UninitializedIpfs::enable_keepalive
• This implementation does not refresh KeepAlive at this time, so once the timer is up, it may close if no other behaviour is keeping the connection open.