S3 Blobstore - provide a blobstore 'prefix' option

As a nexus administrator

I want to have multiple blobstores in one S3 bucket

so that I can use 1 S3 buckets for all my blobstores

Assumptions

At time of writing, the S3 Blobstore assumes that the bucket is exclusive to the blobstore (the content is stored at the root of the bucket).

If we provide administrators the ability to supply a "prefix" for all content in the S3 blobstore, this will allow them to have multiple blobstores sitting in one S3 bucket.

Acceptance Criteria

• The UI presents an option, empty by default, for a content prefix to use. When set, all content for the blobstore is stored under the prefix.

• Using the prefix allows multiple separate blobstores to co-exist in the same S3 bucket.