ui: storage: move node scan selector inside combobox

ui: storage: move node scan selector inside combobox

by converting the relevant selection boxes to combogrids.
This is done to reduce confusion for how/why to select a node, and
doing it this way it is moved closer to the selection of the actual
value we want. It still restricts the nodes when selecting a specific one.

Show it only when there is more than one node according to the
in-memory PVE.data.ResourceStore info, as for single-node setups
there isn't any other node one could scan anyway.

Suggested-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>