Implement auxiliary address store for `DiscoveryBehaviour`

Addresses getting removed from Kademlia for completely innocuous reasons
such as keep-alive timeouts are causing the node to have a lot of dial
failures. The dial failures happen because when `ProtocolController`
tries to connect to a node, and when the address is trying to be fetched
from from `Discovery`, it returns an empty vector since `Kademlia` no
longer holds any addresses for the peer.