Add instrumentation to recompute_head_at_slot (#8049)

Co-Authored-By: Eitan Seri- Levi <eserilev@gmail.com>

beacon_node/store/src/hot_cold_store.rs

@@ -656,6 +656,7 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
     }
 
     /// Fetch a full block with execution payload from the store.
+    #[instrument(skip_all)]
     pub fn get_full_block(
         &self,
         block_root: &Hash256,