[Blocked] Add IPv6 support for UpCloud Terraform module

[Ajarmar]

Description

The UpCloud Terraform module currently only supports IPv4. Add support for IPv6.

Additional context

Updating a node in-place to use IPv6 will restart the node, so it should be configurable per node in order to not restart a whole cluster at once when enabling IPv6.

UpCloud currently does not support IPv6 for:

• Internal networks
• Loadbalancers

We should wait until these are supported before implementing support for IPv6, because otherwise we will have to make another update later.

Definition of done

• IPv6 is supported in the UpCloud Terraform module.

[Ajarmar]

Blocked until UpCloud supports IPv6 for private networks and load balancers.