Add 'generic-microcode' flavor

[Embezzle]

Change Summary

Added generic-microcode flavor which incorporates Intel & AMD microcode packages.
This can be useful in bare metal deployments, where a CPU requires updated microcode to patch vulnerabilities.

Checklist:

• I have read the CONTRIBUTING document

[dmbaturin]

I have nothing against it, but i wonder: is there a reason why we cannot have them in the x86 image by default?

The flavor system supports architecture mix-ins, like https://github.com/vyos/vyos-build/blob/current/data/architectures/amd64.toml
So if the only reason to exclude them is not to clutter images for ARM64 and other architectures with useless files, that would be a perfect place to add them.

Or I'm missing anything and those microcode files can be problematic in some VMs or in some scenarios?

[Embezzle]

I have nothing against it, but i wonder: is there a reason why we cannot have them in the x86 image by default?

The flavor system supports architecture mix-ins, like https://github.com/vyos/vyos-build/blob/current/data/architectures/amd64.toml So if the only reason to exclude them is not to clutter images for ARM64 and other architectures with useless files, that would be a perfect place to add them.

Or I'm missing anything and those microcode files can be problematic in some VMs or in some scenarios?

I strongly agree that microcode should be included in the default generic flavor, but it was unclear to me if the maintainers shared this view. If you are open to this approach, I am happy to send that PR instead.

It should not be an issue if microcode packages are included in VMs, they will simply be ignored. From experience this is not problematic in KVM.

[dmbaturin]

Superseded by vyos/vyos-build#922