Add --semi-supernode support (#8254)

Addresses #8218

A simplified version of #8241 for the initial release.

I've tried to minimise the logic change in this PR, although introducing the `NodeCustodyType` enum still result in quite a bit a of diff, but the actual logic change in `CustodyContext` is quite small.

The main changes are in the `CustdoyContext` struct
* ~~combining `validator_custody_count` and `current_is_supernode` fields into a single `custody_group_count_at_head` field. We persist the cgc of the initial cli values into the `custody_group_count_at_head` field and only allow for increase (same behaviour as before).~~
* I noticed the above approach caused a backward compatibility issue, I've [made a fix](15569bc085) and changed the approach slightly (which was actually what I had originally in mind):
* when initialising, only override the  `validator_custody_count` value if either flag `--supernode` or `--semi-supernode` is used; otherwise leave it as the existing default `0`. Most other logic remains unchanged.

All existing validator custody unit tests are still all passing, and I've added additional tests to cover semi-supernode, and restoring `CustodyContext` from disk.

Note: I've added a `WARN` if the user attempts to switch to a `--semi-supernode` or `--supernode` - this currently has no effect, but once @eserilev column backfill is merged, we should be able to support this quite easily.

Things to test
- [x] cgc in metadata / enr
- [x] cgc in metrics
- [x] subscribed subnets
- [x] getBlobs endpoint


  


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

lighthouse/tests/beacon_node.rs

@@ -4,6 +4,7 @@ use beacon_node::beacon_chain::chain_config::{
     DEFAULT_RE_ORG_MAX_EPOCHS_SINCE_FINALIZATION, DEFAULT_SYNC_TOLERANCE_EPOCHS,
     DisallowedReOrgOffsets,
 };
+use beacon_node::beacon_chain::custody_context::NodeCustodyType;
 use beacon_node::{
     ClientConfig as Config, beacon_chain::graffiti_calculator::GraffitiOrigin,
     beacon_chain::store::config::DatabaseBackend as BeaconNodeBackend,
@@ -782,20 +783,38 @@ fn network_subscribe_all_data_column_subnets_flag() {
     CommandLineTest::new()
         .flag("subscribe-all-data-column-subnets", None)
         .run_with_zero_port()
-        .with_config(|config| assert!(config.network.subscribe_all_data_column_subnets));
+        .with_config(|config| {
+            assert_eq!(config.chain.node_custody_type, NodeCustodyType::Supernode)
+        });
 }
 #[test]
 fn network_supernode_flag() {
     CommandLineTest::new()
         .flag("supernode", None)
         .run_with_zero_port()
-        .with_config(|config| assert!(config.network.subscribe_all_data_column_subnets));
+        .with_config(|config| {
+            assert_eq!(config.chain.node_custody_type, NodeCustodyType::Supernode)
+        });
 }
 #[test]
-fn network_subscribe_all_data_column_subnets_default() {
+fn network_semi_supernode_flag() {
+    CommandLineTest::new()
+        .flag("semi-supernode", None)
+        .run_with_zero_port()
+        .with_config(|config| {
+            assert_eq!(
+                config.chain.node_custody_type,
+                NodeCustodyType::SemiSupernode
+            )
+        });
+}
+#[test]
+fn network_node_custody_type_default() {
     CommandLineTest::new()
         .run_with_zero_port()
-        .with_config(|config| assert!(!config.network.subscribe_all_data_column_subnets));
+        .with_config(|config| {
+            assert_eq!(config.chain.node_custody_type, NodeCustodyType::Fullnode)
+        });
 }
 #[test]
 fn blob_publication_batches() {