ui: node certificate: make parent panel scrollable

ui: node certificate: make parent panel scrollable

The `ACME` panel may be rendered out of sight (overflow) when there
are enough SANs on the upper `Certificates` panel to push it down
enough and the browser/display height is too small.

Enable the `scrollable` config for the parent certificate view panel
to make ExtJS automatically add a scrollbar if the content overflows.

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