localFolderWhitelist for dataset exploring should work for multi-datastore setup

[fm3]

The explore code runs on the wk side. It is not guaranteed that the wk side has access to the same local filesystem as the datastore module.

This means that exploring should (at least for local files) be moved to the datastore entirely, and the wk side should not need to read the config option localFolderWhitelist

This is a follow-up for #7389