S3A: add s3guard command "bucket" to create buckets

cloudstore has an mkbucket command
https://github.com/steveloughran/cloudstore/blob/main/src/main/site/mkbucket.md

however, its v1 api, has problems with spans and needs rework for v2. Oh, and it has not tests.

• move the command into hadoop-aws
• add a test or two,
• add a mapper of 409 to bad request, as "BucketAlreadyOwnedByYouException" comes in as a 409.

Testing will be tricky...as well as not actually wanting to create new buckets, my test a/c doesn't even have the permission to do so.

Proposed tests

1. invalid args must be rejected
2. trying to create the current bucket must be rejected. This happens even if you lack the permission to create

No actual attempts to create a new bucket