Fix custody context initialization race condition that caused panic (#8391)

Take 2 of #8390.

Fixes the race condition properly instead of propagating the error. I think this is a better alternative, and doesn't seem to look that bad.


  * Lift node id loading or generation from `NetworkService ` startup to the `ClientBuilder`, so that it can be used to compute custody columns for the beacon chain without waiting for Network bootstrap.

I've considered and implemented a few alternatives:
1. passing `node_id` to beacon chain builder and compute columns when creating `CustodyContext`. This approach isn't good for separation of concerns and isn't great for testability
2. passing `ordered_custody_groups` to beacon chain. `CustodyContext` only uses this to compute ordered custody columns, so we might as well lift this logic out, so we don't have to do error handling in `CustodyContext` construction. Less tests to update;.


Co-Authored-By: Jimmy Chen <jchen.tc@gmail.com>

beacon_node/network/src/service.rs

@@ -12,6 +12,7 @@ use futures::future::OptionFuture;
 use futures::prelude::*;
 
 use lighthouse_network::Enr;
+use lighthouse_network::identity::Keypair;
 use lighthouse_network::rpc::InboundRequestId;
 use lighthouse_network::rpc::RequestType;
 use lighthouse_network::rpc::methods::RpcResponse;
@@ -212,6 +213,7 @@ impl<T: BeaconChainTypes> NetworkService<T> {
         executor: task_executor::TaskExecutor,
         libp2p_registry: Option<&'_ mut Registry>,
         beacon_processor_send: BeaconProcessorSend<T::EthSpec>,
+        local_keypair: Keypair,
     ) -> Result<
         (
             NetworkService<T>,
@@ -284,6 +286,7 @@ impl<T: BeaconChainTypes> NetworkService<T> {
                 .data_availability_checker
                 .custody_context()
                 .custody_group_count_at_head(&beacon_chain.spec),
+            local_keypair,
         )
         .await?;
 
@@ -366,6 +369,7 @@ impl<T: BeaconChainTypes> NetworkService<T> {
         executor: task_executor::TaskExecutor,
         libp2p_registry: Option<&'_ mut Registry>,
         beacon_processor_send: BeaconProcessorSend<T::EthSpec>,
+        local_keypair: Keypair,
     ) -> Result<(Arc<NetworkGlobals<T::EthSpec>>, NetworkSenders<T::EthSpec>), String> {
         let (network_service, network_globals, network_senders) = Self::build(
             beacon_chain,
@@ -373,6 +377,7 @@ impl<T: BeaconChainTypes> NetworkService<T> {
             executor.clone(),
             libp2p_registry,
             beacon_processor_send,
+            local_keypair,
         )
         .await?;