Implement /lighthouse/custody/info API (#8276)

Closes:

- https://github.com/sigp/lighthouse/issues/8249


  New `/lighthouse/custody` API including:

- [x] Earliest custodied data column slot
- [x] Node CGC
- [x] Custodied columns


Co-Authored-By: Michael Sproul <michael@sigmaprime.io>

consensus/types/src/chain_spec.rs

@@ -255,7 +255,7 @@ pub struct ChainSpec {
      * Networking Fulu
      */
     pub(crate) blob_schedule: BlobSchedule,
-    min_epochs_for_data_column_sidecars_requests: u64,
+    pub min_epochs_for_data_column_sidecars_requests: u64,
 
     /*
      * Networking Gloas