[Feature]: Node/Bastion: add bootmode

[jfbus]

Problem to Solve

Thanks to UEFI, VMs can boot securely using a signed kernel.

Proposed Solution

Add a bootmode (uefi|legacy) attribute to VMs (nodes, bastion).

Additional Context

Secure boot requires an OMI having a signed kernel. The current OSS images do not have a signed kernel.

As OSS images are already UEFI compatible, the VMs can boot using UEFI, even if not securely.

Environment Details

- Kubernetes version (`kubectl version`):
- OS (`/etc/os-release`):
- Kernel (`uname -a`):
- cluster-api-provider-outscale version:
- cluster-api version:
- Install tools:
- Kubernetes distribution:
- Kubernetes distribution version: