Use Floating IPs for bastions on UpCloud

[Xartos]

Proposed feature

Upcloud now supports Floating IPs for private interfaces.
Since that would simplify the machine networking situation and reduce the risk of conflicting routes we should take a look at that and migrate away from using a separate private NIC.

Proposed alternatives

Add FIPs to the private NIC and remove the public NICs for all bastions.

Additional context

No response

Definition of done

• Bastion hosts isn't using public NICs
• Bastion hosts are using FIPs for public access