Adding website endpoint as stored attribute

Adding the website endpoint associated with each bucket as a stored attribute
location_constraint is the AZ in most cases, except it is nil/US for us-east-1, and EU for eu-west-1. Website endpoints are of the format `bucketname.s3-website-#{bucket_az}.amazonaws.com`

Couldn't find an api call that would give me that, so I had to manually derive it.