fix: RetainUntilDate in the correct format

[gribouille]

RetainUntilDate uses the time.RFC3339 format instead of the ISO 8601 format.

This problem generates the error The retain until date must be provided in ISO 8601 format.

[harshavardhana]

who is returning this error? which server @gribouille

[gribouille]

OVHcloud s3 object storage: https://www.ovhcloud.com/en/public-cloud/object-storage/

The problem is similar to: minio/minio#15741

[harshavardhana]

OVHcloud s3 object storage: https://www.ovhcloud.com/en/public-cloud/object-storage/

The problem is similar to: minio/minio#15741

AWS S3 runs fine, this looks like OVH Cloud bug.

[harshavardhana]

And has been for years. I don't think we can take this PR. It looks like server implementation bug.

[harshavardhana]

The problem is similar to: minio/minio#15741

This is not the same problem as here. Server preserves meta is iso9601 format. But it is okay to send it either in iso8601 or rfc3339

[gribouille]

The AWS documentation is not precise but the ISO 8601 seems to be the consensus:

• https://github.com/aws/aws-sdk-go/blob/main/service/s3/s3manager/upload_input.go#L187
• https://www.ibm.com/docs/en/coss/3.17.3?topic=objects-upload-object
• https://infohub.delltechnologies.com/p/better-protection-with-dell-emc-ecs-object-lock-2/
• https://docs.netapp.com/us-en/storagegrid-115/s3/using-s3-object-lock.html#enabling-s3-object-lock-for-a-bucket