HDFS browser displays even files

## Describe the bug
Menas, when choosing Dataset, lets the user choose raw and publish output folders, but displays even normal files. For usability purposes and to lower error chance, this should only display folders.

## Additional context
Maybe even validate the following path is in `/[0-9]{4}/[0-9]{2}/[0-9]{2}/v[0-9]{1}/` like format.

Start by searching the Menas Dataset raw/publish output folder chooser and the HDFS browser entry point. Reproduce the bug by opening that chooser and checking that normal files appear alongside folders. Done means the chooser only displays folders, with any added validation matching the path format described in the issue.

Scritto dal modello di indicizzazione a partire dal testo della issue.