Encode dir obj names before expiration (#19305)

Object names of directory objects qualified for ExpiredObjectAllVersions
must be encoded appropriately before calling on deletePrefix on their
erasure set.

e.g., a directory object and regular objects with overlapping prefixes
could lead to the expiration of regular objects, which is not the 
intention of ILM. 

```
bucket/dir/ ---> directory object
bucket/dir/obj-1
```

When `bucket/dir/` qualifies for expiration, the current implementation would
remove regular objects under the prefix `bucket/dir/`, in this case,
`bucket/dir/obj-1`.

cmd/batch-expire.go

@@ -427,7 +427,7 @@ func batchObjsForDelete(ctx context.Context, r *BatchJobExpire, ri *batchJobInfo
 					default:
 					}
 					stopFn := globalBatchJobsMetrics.trace(batchJobMetricExpire, ri.JobID, attempts)
-					_, err := api.DeleteObject(ctx, exp.Bucket, exp.Name, ObjectOptions{
+					_, err := api.DeleteObject(ctx, exp.Bucket, encodeDirObject(exp.Name), ObjectOptions{
 						DeletePrefix: true,
 					})
 					if err != nil {