Document S3 datastore

The S3 datastore is currently hardly documented.

The generic blobstore documentation is very much focused about the internal class structures, but quite confusing for someone who wants to configure a specific datastore such as file and s3 (the only ones right now). S3 settings are not documented at all, the config page only mentions the generic maxCachedBinarySize and cacheSizeInMB.

The best bet is the Adobe AEM product documentation, but that is for an older version and a few things changed since then.

Specific items below. Some have been confusing people using oak-blob-cloud 1.5.15:

• "secret" property unclear (new)
• secretKey & accessKey can be omitted to leverage IAM roles (new)
• drop of proactiveCaching property (new)
• aws bucket/region/etc. settings
• config options (timeout, retries, threads)
• understanding caching behavior and performance optimization
• shared vs. non-shared options
• migrating from a previous version, how to update the config
• requirements on the AWS (account) side