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>

testing/simulator/src/eth1_sim.rs

@@ -1,3 +1,4 @@
+use crate::local_network::INVALID_ADDRESS;
 use crate::{checks, LocalNetwork, E};
 use clap::ArgMatches;
 use eth1::http::Eth1Id;
@@ -128,8 +129,12 @@ pub fn run_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
         /*
          * One by one, add beacon nodes to the network.
          */
-        for _ in 0..node_count - 1 {
-            network.add_beacon_node(beacon_config.clone()).await?;
+        for i in 0..node_count - 1 {
+            let mut config = beacon_config.clone();
+            if i % 2 == 0 {
+                config.eth1.endpoints.insert(0, INVALID_ADDRESS.to_string());
+            }
+            network.add_beacon_node(config).await?;
         }
 
         /*
@@ -137,7 +142,7 @@ pub fn run_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
          */
         for (i, files) in validator_files.into_iter().enumerate() {
             network
-                .add_validator_client(testing_validator_config(), i, files)
+                .add_validator_client(testing_validator_config(), i, files, i % 2 == 0)
                 .await?;
         }