Changes to Create backup

removed the optional property backup/s3_path from the response with the 201 status

added the new pending enum value to the backup/status response property for the response status 201

the backup/backup_timestamp response's property format changed from date-time to no format for status 201

the backup/completed_at response's property format changed from date-time to no format for status 201

the backup/expires_at response's property format changed from date-time to no format for status 201

added the optional property backup/restorable to the response with the 201 status

added the optional property backup/restore_window_start to the response with the 201 status

endpoint added