Make custom kernel build with custom configuration

[573]

Regarding

@Atemu

I’d highly recommend you use extraStructuredConfig like this:

@julm

Note that the equivalent of structuredExtraConfig is called extraStructuredConfig in kernelPatches

extraStructuredConfig is what it is called only inside the kernelPatches closure. For all other occasions use structuredExtraConfig please. I myself needed two days to spot this difference in detail.