Validator registration request failures do not cause us to mark BNs offline (#3488)

## Issue Addressed

Relates to https://github.com/sigp/lighthouse/issues/3416

## Proposed Changes

- Add an `OfflineOnFailure` enum to the `first_success` method for querying beacon nodes so that a val registration request failure from the BN -> builder does not result in the BN being marked offline. This seems important because these failures could be coming directly from a connected relay and actually have no bearing on BN health.  Other messages that are sent to a relay have a local fallback so shouldn't result in errors 

- Downgrade the following log to a `WARN`

```
ERRO Unable to publish validator registrations to the builder network, error: All endpoints failed https://BN_B => RequestFailed(ServerMessage(ErrorMessage { code: 500, message: "UNHANDLED_ERROR: BuilderMissing", stacktraces: [] })), https://XXXX/ => Unavailable(Offline), [omitted]
```

## Additional Info

I think this change at least improves the UX of having a VC connected to some builder and some non-builder beacon nodes. I think we need to balance potentially alerting users that there is a BN <> VC misconfiguration and also allowing this type of fallback to work. 

If we want to fully support this type of configuration we may want to consider adding a flag `--builder-beacon-nodes` and track whether a VC should be making builder queries on a per-beacon node basis.  But I think the changes in this PR are independent of that type of extension.

PS: Sorry for the big diff here, it's mostly formatting changes after I added a new arg to a bunch of methods calls.




Co-authored-by: realbigsean <sean@sigmaprime.io>

validator_client/src/duties_service/sync.rs

@@ -1,3 +1,4 @@
+use crate::beacon_node_fallback::OfflineOnFailure;
 use crate::{
     doppelganger_service::DoppelgangerStatus,
     duties_service::{DutiesService, Error},
@@ -420,11 +421,15 @@ pub async fn poll_sync_committee_duties_for_period<T: SlotClock + 'static, E: Et
 
     let duties_response = duties_service
         .beacon_nodes
-        .first_success(duties_service.require_synced, |beacon_node| async move {
-            beacon_node
-                .post_validator_duties_sync(period_start_epoch, local_indices)
-                .await
-        })
+        .first_success(
+            duties_service.require_synced,
+            OfflineOnFailure::Yes,
+            |beacon_node| async move {
+                beacon_node
+                    .post_validator_duties_sync(period_start_epoch, local_indices)
+                    .await
+            },
+        )
         .await;
 
     let duties = match duties_response {