Add metrics for EE PayloadStatus returns (#3486)

## Issue Addressed

NA

## Proposed Changes

Adds some metrics so we can track payload status responses from the EE. I think this will be useful for troubleshooting and alerting.

I also bumped the `BecaonChain::per_slot_task` to `debug` since it doesn't seem too noisy and would have helped us with some things we were debugging in the past.

## Additional Info

NA

beacon_node/execution_layer/src/lib.rs

@@ -893,6 +893,13 @@ impl<T: EthSpec> ExecutionLayer<T> {
             .request(|engine| engine.api.new_payload_v1(execution_payload.clone()))
             .await;
 
+        if let Ok(status) = &result {
+            metrics::inc_counter_vec(
+                &metrics::EXECUTION_LAYER_PAYLOAD_STATUS,
+                &["new_payload", status.status.into()],
+            );
+        }
+
         process_payload_status(execution_payload.block_hash, result, self.log())
             .map_err(Box::new)
             .map_err(Error::EngineError)
@@ -1032,6 +1039,13 @@ impl<T: EthSpec> ExecutionLayer<T> {
             })
             .await;
 
+        if let Ok(status) = &result {
+            metrics::inc_counter_vec(
+                &metrics::EXECUTION_LAYER_PAYLOAD_STATUS,
+                &["forkchoice_updated", status.payload_status.status.into()],
+            );
+        }
+
         process_payload_status(
             head_block_hash,
             result.map(|response| response.payload_status),