Introduce 'virt-what-cvm' program

Introduce 'virt-what-cvm' program

The 'virt-what' program prints facts that reflect the hypervisor that
the guest is running under.

The new complementary 'virt-what-cvm' program prints facts that reflect
the confidential virtualization technology the guest is running under,
if any.

It is kept as a separate tool, rather than incorporating the facts into
'virt-what' output because it is considering a different aspect of the
virtualization. Furthermore there are specific security concerns around
the usage of facts reported by 'virt-what-cvm'.

The tool has been tested in a number of environments

 * Azure confidential guest with AMD SEV-SNP (GA)
 * Azure confidential guest with Intel TDX (technology preview)
 * Fedora 37 QEMU/KVM guest with AMD SEV (GA)
 * Fedora 37 QEMU/KVM guest with AMD SEV-ES (GA)
 * Fedora 38 QEMU/KVM guest with AMD SEV-SNP + SVSM (devel snapshot)

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>