Use events API to eager send attestations (#7892)

Co-Authored-By: hopinheimer <knmanas6@gmail.com>

Co-Authored-By: hopinheimer <48147533+hopinheimer@users.noreply.github.com>

Co-Authored-By: Eitan Seri-Levi <eserilev@ucsc.edu>

Co-Authored-By: Michael Sproul <michael@sigmaprime.io>

Co-Authored-By: Michael Sproul <michaelsproul@users.noreply.github.com>

validator_client/src/cli.rs

@@ -476,6 +476,17 @@ pub struct ValidatorClient {
     )]
     pub beacon_nodes_sync_tolerances: Vec<u64>,
 
+    #[clap(
+        long,
+        help = "Disable the beacon head monitor which tries to attest as soon as any of the \
+                configured beacon nodes sends a head event. Leaving the service enabled is \
+                recommended, but disabling it can lead to reduced bandwidth and more predictable \
+                usage of the primary beacon node (rather than the fastest BN).",
+        display_order = 0,
+        help_heading = FLAG_HEADER
+    )]
+    pub disable_beacon_head_monitor: bool,
+
     #[clap(
         long,
         help = "Disable Lighthouse's slashing protection for all web3signer keys. This can \