Close #2262: Add noVNC scale setting

Close #2262: Add noVNC scale setting

Add a setting to choose the scale mode of the noVNC pop-up as well as
the embedded console in the content panel to "My Settings". Having both
set to local scaling was the most important use-case for the users. One
setting for both places is the simplest solution making this possible.

The new section (fieldset) makes adding further options such as
"Local Cursor" easy.

Co-developed-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Signed-off-by: Dominic Jäger <d.jaeger@proxmox.com>