Add more eth1 metrics (#728)

* Add metrics for junk eth1 votes

* Add eth1 cache metrics

beacon_node/beacon_chain/src/metrics.rs

@@ -153,6 +153,12 @@ lazy_static! {
     pub static ref CHECKPOINT_CACHE_MISSES: Result<IntCounter> =
         try_create_int_counter("beacon_checkpoint_cache_misses_total", "Count of times checkpoint cache fulfils request");
 
+    /*
+     * Eth1
+     */
+    pub static ref JUNK_ETH1_VOTES: Result<IntCounter> =
+        try_create_int_counter("beacon_eth1_junk_votes", "Count of times we have voted junk for eth1 dat");
+
     /*
      * Chain Head
      */