decouple eth2 from store and lighthouse_network (#6680)

- #6452 (partially)


  Remove dependencies on `store` and `lighthouse_network`  from `eth2`. This was achieved as follows:

- depend on `enr` and `multiaddr` directly instead of using `lighthouse_network`'s reexports.
- make `lighthouse_network` responsible for converting between API and internal types.
- in two cases, remove complex internal types and use the generic `serde_json::Value` instead - this is not ideal, but should be fine for now, as this affects two internal non-spec endpoints which are meant for debugging, unstable, and subject to change without notice anyway. Inspired by #6679. The alternative is to move all relevant types to `eth2` or `types` instead - what do you think?

beacon_node/http_api/src/peer.rs

@@ -0,0 +1,13 @@
+use lighthouse_network::PeerInfo;
+use serde::Serialize;
+use types::EthSpec;
+
+/// Information returned by `peers` and `connected_peers`.
+#[derive(Debug, Clone, Serialize)]
+#[serde(bound = "E: EthSpec")]
+pub(crate) struct Peer<E: EthSpec> {
+    /// The Peer's ID
+    pub peer_id: String,
+    /// The PeerInfo associated with the peer.
+    pub peer_info: PeerInfo<E>,
+}