Browse the local file system / bucket for imports

[manthey]

Currently, you have to type the local path or bucket and path to perform an import.

It would be easier if we could browse the local filesystem or the S3 bucket and present a UI for picking the path. For the local filesystem, this could probably be limited to filesystem mount points inside a docker. Outside of a docker, I'm not sure how to apply a sensible limit to what is shown.