Add more eth1 metrics (#728)

* Add metrics for junk eth1 votes

* Add eth1 cache metrics

beacon_node/eth1/src/metrics.rs

@@ -0,0 +1,19 @@
+pub use lighthouse_metrics::*;
+
+lazy_static! {
+    /*
+     * Eth1 blocks
+     */
+    pub static ref BLOCK_CACHE_LEN: Result<IntGauge> =
+        try_create_int_gauge("eth1_block_cache_len", "Count of eth1 blocks in cache");
+    pub static ref LATEST_CACHED_BLOCK_TIMESTAMP: Result<IntGauge> =
+        try_create_int_gauge("eth1_latest_cached_block_timestamp", "Timestamp of latest block in eth1 cache");
+
+    /*
+     * Eth1 deposits
+     */
+    pub static ref DEPOSIT_CACHE_LEN: Result<IntGauge> =
+        try_create_int_gauge("eth1_deposit_cache_len", "Number of deposits in the eth1 cache");
+    pub static ref HIGHEST_PROCESSED_DEPOSIT_BLOCK: Result<IntGauge> =
+        try_create_int_gauge("eth1_highest_processed_deposit_block", "Number of the last block checked for deposits");
+}