Use head state in validator API #8

Computing the preprocessed state fails when the app is freshly started and has too many empty slots,
preventing it from signing voluntary exits. This necessitates changing the signing process to use the head instead
of the preprocessed state.

validator/src/api.rs

@@ -628,7 +628,7 @@ async fn keymanager_create_voluntary_exit<P: Preset, W: Wait>(
     EthPath(pubkey): EthPath<PublicKeyBytes>,
     EthQuery(query): EthQuery<CreateVoluntaryExitQuery>,
 ) -> Result<EthResponse<SignedVoluntaryExit>, Error> {
-    let state = controller.preprocessed_state_at_current_slot()?;
+    let state = controller.head_state().value;
 
     let epoch = query
         .epoch