Expose SMBIOS options

[satwell]

Is your feature request related to a problem? Please describe.
I'd like to control a VM's SMBIOS settings through Terraform. These are available as smbios1 in the PVE API.

The SMBIOS settings are useful for plumbing metadata and config information through to a VM. In particular, cloud-init allows you to specify a network metadata source for NoCloud using the SMBIOS serial number. This can be more flexible in some situations than using PVE's built-in cloud-init support.

Describe the solution you'd like
An smbios_settings block in the proxmox_virtual_environment_vm resource that controls the VM's SMBIOS settings.

Describe alternatives you've considered
None.

Additional context
It looks like there's already some initial code for this in vm_types.go, but it doesn't look like it's available in the resource.