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/lighthouse_network/src/rpc/mod.rs

@@ -26,7 +26,7 @@ pub(crate) use protocol::InboundRequest;
 pub use handler::SubstreamId;
 pub use methods::{
     BlocksByRangeRequest, BlocksByRootRequest, GoodbyeReason, LightClientBootstrapRequest,
-    MaxRequestBlocks, RPCResponseErrorCode, ResponseTermination, StatusMessage, MAX_REQUEST_BLOCKS,
+    RPCResponseErrorCode, ResponseTermination, StatusMessage,
 };
 pub(crate) use outbound::OutboundRequest;
 pub use protocol::{max_rpc_size, Protocol, RPCError};