feat(kad): deprecate Config::set_connection_idle_timeout

[leonzchang]

Description

Related: #3844.
Related: #4659.

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[leonzchang]

rust-libp2p/protocols/kad/src/behaviour.rs

Lines 1896 to 1913 in b00a8b9

	fn on_connection_established(
	&mut self,
	ConnectionEstablished {
	peer_id,
	failed_addresses,
	other_established,
	..
	}: ConnectionEstablished,
	) {
	for addr in failed_addresses {
	self.address_failed(peer_id, addr);
	}
	// Peer's first connection.
	if other_established == 0 {
	self.connected_peers.insert(peer_id);
	}
	}

This may need to be changed when the #4659 (comment) is confirmed.

[thomaseizinger]

Thank you for all the help!