replace instant with web-time (#5800)

* replace instant with web_time

* Merge branch 'unstable' into replace-instant-gossipsub

# Conflicts:
#	Cargo.lock
#	beacon_node/lighthouse_network/Cargo.toml

beacon_node/lighthouse_network/gossipsub/src/backoff.rs

@@ -20,13 +20,13 @@
 
 //! Data structure for efficiently storing known back-off's when pruning peers.
 use crate::topic::TopicHash;
-use instant::Instant;
 use libp2p::identity::PeerId;
 use std::collections::{
     hash_map::{Entry, HashMap},
     HashSet,
 };
 use std::time::Duration;
+use web_time::Instant;
 
 #[derive(Copy, Clone)]
 struct HeartbeatIndex(usize);