Remove `DisplayName` from S3Mock

[afranken]

S3 APIs display a deprecation notice:

Important

End of support notice: Beginning November 21, 2025, Amazon S3 will stop returning DisplayName. Update your applications to use canonical > IDs (unique identifier for AWS accounts), AWS account ID (12 digit identifier) or IAM ARNs (full resource naming) as a direct replacement of DisplayName.

Between July 15, 2025 and November 21, 2025, you will begin to see an increasing rate of missing DisplayName in the Owner object.

This change affects the following AWS Regions: US East (N. Virginia) Region, US West (N. California) Region, US West (Oregon) Region, Asia Pacific (Singapore) Region, Asia Pacific (Sydney) Region, Asia Pacific (Tokyo) Region, Europe (Ireland) Region, and South America (São Paulo) Region.

Make sure S3Mock doesn't return the DisplayName attribute.
See
https://github.com/adobe/S3Mock/blob/main/server/src/main/java/com/adobe/testing/s3mock/dto/CanonicalUser.java#L29
https://github.com/adobe/S3Mock/blob/main/server/src/main/java/com/adobe/testing/s3mock/dto/Owner.java#L30