HPCC-12075 Allow to select a good landing zone for Upload/download

When the Upload/download File menu is selected, FileSpray.DropZoneFiles
service tries to retrieve files from the first landing zone. If the
dafilesrv is down on that landing zone, after several retries (a long
time wait), an exception is sent out and the use cannot access any
landing zone. This fix displays landing zone list after the Upload/
download File menu is clicked. A user may choose any landing zone for
file upload and download.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>

HPCC-12075 WIP

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>