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/no_eth1_sim.rs

@@ -103,7 +103,7 @@ pub fn run_no_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
         let add_validators_fut = async {
             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?;
             }