Remove lighthouse_network dependency from eth2 crate

[pawanjay176]

Issue Addressed

N/A

Proposed Changes

The eth2 which contains our http api client crate depends on the lighthouse_network crate for some networking types.
This is completely unnecessary imo because we can just return strings/serde_json::Value types for the networking types.
These types don't require us using any of the functions on the type structs. They just exist for some typing.

This is an enormous source of pain for any dependency that pulls the eth2 crate for using a BeaconNodeHttpClient because importing lighthouse_network pulls in a bunch of other dependencies that just bloats the dep tree.

I don't see any reason why the networking related types cannot be represented as String or json values. Let me know if that is not the case.

Todo

• Test all affected endpoints

[AgeManning]

The same as this? #6452

[pawanjay176]

Yeah there's already work being done on this. I'm closing this for now