doc: rgw document s3 bucket location features

Fixes: #10142
Reported-by: Neil Levine <nlevine@redhat.com>
Signed-off-by: Abhishek Lekshmanan <abhishek.lekshmanan@ril.com>
Merge pull request #2998 from theanalyst/doc/rgw-s3-bucket-loc

doc: rgw document s3 bucket location features.

Reviewed-by: John Wilkins <jowilkin@redhat.com>