Add Tags to buckets and objects

Tags in S3 are used to identify different groups of data. Permissions can be set on these tags.

So the corresponding headers can be read and additional metadata added to the created phobos objects. Afterwards some permission checking can be added as well.

And after all that is done we can think about who will ever actually use this functionality...

For more information, see https://docs.aws.amazon.com/AmazonS3/latest/dev/object-tagging.html