Runtime rpc request sizes (#4841)

* add runtime variable list type

* add configs to ChainSpec

* git rid of max request blocks type

* fix tests and lints

* remove todos

* git rid of old const usage

* fix decode impl

* add new config to `Config` api struct

* add docs fix compilt

* move methods for per-fork-spec to chainspec

* get values off chain spec

* fix compile

* remove min by root size

* add tests for runtime var list

---------

Co-authored-by: Jimmy Chen <jchen.tc@gmail.com>

beacon_node/network/src/sync/manager.rs

@@ -52,7 +52,6 @@ use beacon_chain::{
     AvailabilityProcessingStatus, BeaconChain, BeaconChainTypes, BlockError, EngineState,
 };
 use futures::StreamExt;
-use lighthouse_network::rpc::methods::MAX_REQUEST_BLOCKS;
 use lighthouse_network::rpc::RPCError;
 use lighthouse_network::types::{NetworkGlobals, SyncState};
 use lighthouse_network::SyncInfo;
@@ -230,7 +229,7 @@ pub fn spawn<T: BeaconChainTypes>(
     log: slog::Logger,
 ) {
     assert!(
-        MAX_REQUEST_BLOCKS >= T::EthSpec::slots_per_epoch() * EPOCHS_PER_BATCH,
+        beacon_chain.spec.max_request_blocks >= T::EthSpec::slots_per_epoch() * EPOCHS_PER_BATCH,
         "Max blocks that can be requested in a single batch greater than max allowed blocks in a single request"
     );