Add Gloas boilerplate (#7728)

Adds the required boilerplate code for the Gloas (Glamsterdam) hard fork. This allows PRs testing Gloas-candidate features to test fork transition.

This also includes de-duplication of post-Bellatrix readiness notifiers from #6797 (credit to @dapplion)

consensus/state_processing/src/per_slot_processing.rs

@@ -1,6 +1,6 @@
 use crate::upgrade::{
     upgrade_to_altair, upgrade_to_bellatrix, upgrade_to_capella, upgrade_to_deneb,
-    upgrade_to_electra, upgrade_to_fulu,
+    upgrade_to_electra, upgrade_to_fulu, upgrade_to_gloas,
 };
 use crate::{per_epoch_processing::EpochProcessingSummary, *};
 use safe_arith::{ArithError, SafeArith};
@@ -78,6 +78,11 @@ pub fn per_slot_processing<E: EthSpec>(
             upgrade_to_fulu(state, spec)?;
         }
 
+        // Gloas.
+        if spec.gloas_fork_epoch == Some(state.current_epoch()) {
+            upgrade_to_gloas(state, spec)?;
+        }
+
         // Additionally build all caches so that all valid states that are advanced always have
         // committee caches built, and we don't have to worry about initialising them at higher
         // layers.