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/sync_committee_rewards.rs

@@ -1,7 +1,6 @@
 use crate::{BlockId, ExecutionOptimistic};
 use beacon_chain::{BeaconChain, BeaconChainError, BeaconChainTypes};
-use eth2::lighthouse::SyncCommitteeReward;
-use eth2::types::ValidatorId;
+use eth2::types::{SyncCommitteeReward, ValidatorId};
 use state_processing::BlockReplayer;
 use std::sync::Arc;
 use tracing::debug;