Upgrade to tokio 0.3 (#1839)

## Description

This PR updates Lighthouse to tokio 0.3. It includes a number of dependency updates and some structural changes as to how we create and spawn tasks.

This also brings with it a number of various improvements:

- Discv5 update
- Libp2p update
- Fix for recompilation issues
- Improved UPnP port mapping handling
- Futures dependency update
- Log downgrade to traces for rejecting peers when we've reached our max



Co-authored-by: blacktemplar <blacktemplar@a1.net>

validator_client/src/http_api/create_validator.rs

@@ -21,7 +21,7 @@ use validator_dir::Builder as ValidatorDirBuilder;
 ///
 /// If `key_derivation_path_offset` is supplied then the EIP-2334 validator index will start at
 /// this point.
-pub fn create_validators<P: AsRef<Path>, T: 'static + SlotClock, E: EthSpec>(
+pub async fn create_validators<P: AsRef<Path>, T: 'static + SlotClock, E: EthSpec>(
     mnemonic_opt: Option<Mnemonic>,
     key_derivation_path_offset: Option<u32>,
     validator_requests: &[api_types::ValidatorRequest],
@@ -129,12 +129,9 @@ pub fn create_validators<P: AsRef<Path>, T: 'static + SlotClock, E: EthSpec>(
         let voting_keystore_path = validator_dir.voting_keystore_path();
         drop(validator_dir);
 
-        tokio::runtime::Handle::current()
-            .block_on(validator_store.add_validator_keystore(
-                voting_keystore_path,
-                voting_password_string,
-                request.enable,
-            ))
+        validator_store
+            .add_validator_keystore(voting_keystore_path, voting_password_string, request.enable)
+            .await
             .map_err(|e| {
                 warp_utils::reject::custom_server_error(format!(
                     "failed to initialize validator: {:?}",