Enforce bucket naming rules

[ChrisSchinnerl]

While we are preparing the API for v2 it might make sense to enforce some stricter rules on bucket names. To remain compatible with S3 we should use their rules as a reference. From what I can see it should be pretty sane to implement the first 5 rules they list.

Then we can also change the varchar(255) for the bucket name to a varchar(63). I'm not sure if they allow UTF-16 but in that case we might need to adjust the column length to account for that.

https://docs.aws.amazon.com/AmazonS3/latest/userguide/bucketnamingrules.html