Validate bucket names as per revised s3 spec

Validate bucket names as per revised s3 spec

As per amazon s3 spec -
https://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html

* The s3 bucket names should not contain upper case letters or underscore.
* Name cannot end with dash or have consecutive periods, or dashes adjacent
  to periods.
* Each label in the bucket name must start and end with a lowercase
  letter or a number.
* Name cannot exceed 63 characters.

This change is to enforce these rules if rgw_relaxed_s3_bucket_names is set to
'false' which is by default.

Fixes: https://tracker.ceph.com/issues/36293
Signed-off-by: Soumya Koduri <skoduri@redhat.com>