Hi,
I haven't found a global option to set this.
You'll have to do it vm after vm, which isn't a bad thing in my opinion as
you'll have to reboot every vm after enabling HA anyways.
For new VMs depending on your workflow I'd create a template or an instance type with
HA enabled.
You can also enable HA in the preset instance types via "Administration" >
"Configure" > "Instance Types". Keep in mind that you will have to
enable advanced options to see the High Avalibitity tab.
Best regards,
Tivon