Reorg events (#2090)

## Issue Addressed

Resolves #2088

## Proposed Changes

Add the `chain_reorg` SSE event topic

## Additional Info


Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: Paul Hauner <paul@paulhauner.com>

beacon_node/http_api/src/lib.rs

@@ -2153,6 +2153,9 @@ pub fn serve<T: BeaconChainTypes>(
                                 api_types::EventTopic::FinalizedCheckpoint => {
                                     event_handler.subscribe_finalized()
                                 }
+                                api_types::EventTopic::ChainReorg => {
+                                    event_handler.subscribe_reorgs()
+                                }
                             };
 
                             receivers.push(BroadcastStream::new(receiver).map(|msg| {