BN Fallback v2 (#2080)

## Issue Addressed

- Resolves #1883

## Proposed Changes

This follows on from @blacktemplar's work in #2018.

- Allows the VC to connect to multiple BN for redundancy.
  - Update the simulator so some nodes always need to rely on their fallback.
- Adds some extra deprecation warnings for `--eth1-endpoint`
- Pass `SignatureBytes` as a reference instead of by value.

## Additional Info

NA

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

beacon_node/http_api/tests/tests.rs

@@ -1643,7 +1643,7 @@ impl ApiTester {
 
             let block = self
                 .client
-                .get_validator_blocks::<E>(slot, randao_reveal, None)
+                .get_validator_blocks::<E>(slot, &randao_reveal, None)
                 .await
                 .unwrap()
                 .data;

beacon_node/src/config.rs

@@ -170,6 +170,11 @@ pub fn get_config<E: EthSpec>(
 
     // Defines the URL to reach the eth1 node.
     if let Some(val) = cli_args.value_of("eth1-endpoint") {
+        warn!(
+            log,
+            "The --eth1-endpoint flag is deprecated";
+            "msg" => "please use --eth1-endpoints instead"
+        );
         client_config.sync_eth1_chain = true;
         client_config.eth1.endpoints = vec![val.to_string()];
     } else if let Some(val) = cli_args.value_of("eth1-endpoints") {