File Browser: Symlink following lets scoped users read, overwrite, and share files outside their filebrowser scope

Summary File Browser enforces per-user scope with afero.NewBasePathFsafero.NewOsFs, scope, set up in users/users.go. This blocks lexical ../ traversal, but it does not stop the HTTP file handlers from following symbolic links before they open, serve, write, share, or list a file. As a result, a...