[fix][ml] Corrected pulsar_storage_size metric to not multiply offloaded storage by the write quorum (#24054)

(cherry picked from commit 1309cba)

Author: dlg99

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerMBeanImpl.java

@@ -322,7 +322,10 @@ public double getLedgerSwitchLatencyAverageUsec() {
 
     @Override
     public long getStoredMessagesSize() {
-        return managedLedger.getTotalSize() * managedLedger.getConfig().getWriteQuorumSize();
+        long totalSize = managedLedger.getTotalSize();
+        long offloadedSize = managedLedger.getOffloadedSize();
+        long bookieSize = totalSize - offloadedSize;
+        return bookieSize * managedLedger.getConfig().getWriteQuorumSize() + offloadedSize;
     }
 
     @Override