Comment 0 for bug 1990504

[Impact]
nullboot 0.4.0 adds an additional feature necessary for enablement of the target platform: writing JSON files with the boot order during image building, so that the boot entries can be configured at first booth.

I also correctly handles the case where the BootOrder variable was deleted by populating it, instead of producing an error which IIRC was also seen as part of the validation, but also significantly improves testing.

[Test plan]
Gauthier Jolly will build images with the proposed package and boot them on Azure CVM.

[Where problems could occur]
The potential for regressions is low as the new code path uses the mock EFI variables implementation that the test suite uses, and is just a couple of ifs in the main code.

Any failure to write JSON files during image build can easily be worked around by disabling that bit in the image building script, first boot would be slower, so they are not exactly fatal.

If people relied on missing BootOrder producing an error, they see a change in behavior.

It is unlikely anyone is using that in jammy, as it is closely tied to Azure CVM, and we only enabled focal so far, so overall I think nobody should be broken even if there were an issue.