HDDS-15618. Fix ListObjects to include single whitespace-only S3 object keys

[Gargi-jais11]

What changes were proposed in this pull request?

s3-tests test_bucket_create_special_key_names fails because a key named **' '** is created but not returned by ListObjects. OmMetadataManagerImpl.getOzoneKey() uses StringUtils.isNotBlank(), which treats whitespace-only keys as absent, so the object is stored under /volume/bucket instead of /volume/bucket/.
List object uses prefix /volume/bucket/, so the key is omitted. Fix key encoding to allow whitespace-only names

Expected: [' ', '"', '$', '%', '&', "'", '<', '>', '_', '_ ', '_ _', '__']
Actual:   ['"', '$', '%', '&', "'", '<', '>', '_', '_ ', '_ _'] 

  # missing leading ' '

At index 0: ' ' != '"' 

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-15618

How was this patch tested?

Added unit test.

[priyeshkaratha]

Thanks @Gargi-jais11 for the patch. Changes LGTM

[ivandika3]

Thanks @Gargi-jais11 , left one comment.

[ivandika3]

I'd prefer if we actually have an S3 integration test to prove that Ozone actually accepts a blank key (I'm not sure if it does). If OM does not accept a blank key, then the S3 single white space case will never be exercised.

[chungen0126]

Thanks @Gargi-jais11 for working on this.

As far as I know, HDFS doesn't support filenames with spaces. I'm concerning about how this change impact that. Have you looked into it?