fix #6113: ui: import: add pool selector

There is no option to select a resource pool when importing a guest from
OVA or VMware/ESXi.

Add the pvePoolSelector to the guest import window.

Remove spacer to align rows.

Signed-off-by: Elias Huhsovitz <e.huhsovitz@proxmox.com>
Link: https://lore.proxmox.com/20260820124601.135875-1-e.huhsovitz@proxmox.com