ntp_callbacks: Switch to chunked_hash_map

For super high partition topics at high partition density these can lead
to oversized allocs due to the use of `absl::flat_hash_map`.

Switch to chunked_hash_map.

src/v/cluster/ntp_callbacks.h

@@ -12,10 +12,9 @@
 #pragma once
 
 #include "cluster/notification.h"
+#include "container/chunked_hash_map.h"
 #include "model/fundamental.h"
 
-#include <absl/container/flat_hash_map.h>
-
 namespace cluster {
 
 /**
@@ -148,7 +147,7 @@ class ntp_callbacks {
     template<typename Key, typename Value>
     struct node {
         callbacks_t callbacks;
-        absl::flat_hash_map<Key, Value> next;
+        chunked_hash_map<Key, Value> next;
     };
 
     notification_id_type