Reduce eth2 dependency space (#8524)

Remove certain dependencies from `eth2`, and feature-gate others which are only used by certain endpoints.

| Removed | Optional | Dev only |
| -------- | -------- | -------- |
| `either` `enr` `libp2p-identity` `multiaddr` | `protoarray` `eth2_keystore` `eip_3076` `zeroize` `reqwest-eventsource` `futures` `futures-util` | `rand` `test_random_derive` |

This is done by adding an `events` feature which enables the events endpoint and its associated dependencies.
The `lighthouse` feature also enables its associated dependencies making them optional.

The networking-adjacent dependencies were removed by just having certain fields use a `String` instead of an explicit network type. This means the user should handle conversion at the call site instead. This is a bit spicy, but I believe `PeerId`, `Enr` and `Multiaddr` are easily converted to and from `String`s so I think it's fine and reduces our dependency space by a lot. The alternative is to feature gate these types behind a `network` feature instead.


Co-Authored-By: Mac L <mjladson@pm.me>

beacon_node/http_api/tests/tests.rs

@@ -2853,9 +2853,19 @@ impl ApiTester {
 
         let expected = IdentityData {
             peer_id: self.local_enr.peer_id().to_string(),
-            enr: self.local_enr.clone(),
-            p2p_addresses: self.local_enr.multiaddr_p2p_tcp(),
-            discovery_addresses: self.local_enr.multiaddr_p2p_udp(),
+            enr: self.local_enr.to_base64(),
+            p2p_addresses: self
+                .local_enr
+                .multiaddr_p2p_tcp()
+                .iter()
+                .map(|a| a.to_string())
+                .collect(),
+            discovery_addresses: self
+                .local_enr
+                .multiaddr_p2p_udp()
+                .iter()
+                .map(|a| a.to_string())
+                .collect(),
             metadata: MetaData::V2(MetaDataV2 {
                 seq_number: 0,
                 attnets: "0x0000000000000000".to_string(),
@@ -2884,7 +2894,7 @@ impl ApiTester {
     pub async fn test_get_node_peers_by_id(self) -> Self {
         let result = self
             .client
-            .get_node_peers_by_id(self.external_peer_id)
+            .get_node_peers_by_id(&self.external_peer_id.to_string())
             .await
             .unwrap()
             .data;