Add interop metrics (#2645)

## Issue Addressed

Resolves: #2644

## Proposed Changes

- Adds mandatory metrics mentioned here: https://github.com/ethereum/beacon-metrics/blob/master/metrics.md#interop-metrics

## Additional Info

Couldn't figure out how to alias metrics, so I created them all as new gauges/counters.

Co-authored-by: realbigsean <seananderson33@gmail.com>

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -2953,6 +2953,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             }
 
             metrics::inc_counter(&metrics::FORK_CHOICE_REORG_COUNT);
+            metrics::inc_counter(&metrics::FORK_CHOICE_REORG_COUNT_INTEROP);
             warn!(
                 self.log,
                 "Beacon chain re-org";