fix: decommission delete markers for non-current objects (#15225)

versioned buckets were not creating the delete markers
present in the versioned stack of an object, this essentially
would stop decommission to succeed.

This PR fixes creating such delete markers properly during
a decommissioning process, adds tests as well.

cmd/erasure-server-pool-decom.go

@@ -689,6 +689,7 @@ func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool
 							VersionID:         version.VersionID,
 							MTime:             version.ModTime,
 							DeleteReplication: version.ReplicationState,
+							DeleteMarker:      true, // make sure we create a delete marker
 						})
 					var failure bool
 					if err != nil {
@@ -698,10 +699,10 @@ func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool
 					z.poolMetaMutex.Lock()
 					z.poolMeta.CountItem(idx, 0, failure)
 					z.poolMetaMutex.Unlock()
-					if failure {
-						break // break out on first error
+					if !failure {
+						// Success keep a count.
+						decommissionedCount++
 					}
-					decommissionedCount++
 					continue
 				}