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>

beacon_node/http_api/tests/tests.rs

@@ -1,3 +1,4 @@
+use beacon_chain::custody_context::NodeCustodyType;
 use beacon_chain::test_utils::RelativeSyncCommittee;
 use beacon_chain::{
     BeaconChain, ChainConfig, StateSkipConfig, WhenSlotSkipped,
@@ -90,7 +91,7 @@ struct ApiTester {
 struct ApiTesterConfig {
     spec: ChainSpec,
     retain_historic_states: bool,
-    import_all_data_columns: bool,
+    node_custody_type: NodeCustodyType,
 }
 
 impl Default for ApiTesterConfig {
@@ -100,7 +101,7 @@ impl Default for ApiTesterConfig {
         Self {
             spec,
             retain_historic_states: false,
-            import_all_data_columns: false,
+            node_custody_type: NodeCustodyType::Fullnode,
         }
     }
 }
@@ -139,7 +140,7 @@ impl ApiTester {
             .deterministic_withdrawal_keypairs(VALIDATOR_COUNT)
             .fresh_ephemeral_store()
             .mock_execution_layer()
-            .import_all_data_columns(config.import_all_data_columns)
+            .node_custody_type(config.node_custody_type)
             .build();
 
         harness
@@ -7842,8 +7843,7 @@ async fn get_blobs_post_fulu_supernode() {
     let mut config = ApiTesterConfig {
         retain_historic_states: false,
         spec: E::default_spec(),
-        // For supernode, we import all data columns
-        import_all_data_columns: true,
+        node_custody_type: NodeCustodyType::Supernode,
     };
     config.spec.altair_fork_epoch = Some(Epoch::new(0));
     config.spec.bellatrix_fork_epoch = Some(Epoch::new(0));