Require matching architecture for bootable images

[cgwalters]

xref containers/bootc#682

[mvo5]

Just to double check my understanding: bootc-image-builder --target-arch is not affected here because bib does the foreign arch container pulling and when we run bootc it is already a "foreign" arch binary(?)

[cgwalters]

Just to double check my understanding: bootc-image-builder --target-arch is not affected here because bib does the foreign arch container pulling and when we run bootc it is already a "foreign" arch binary(?)

That sounds right yes. (Using the term both "target" and "foreign" here is a bit confusing; I think we can just say: bib pulls the image with the target arch, and when we run bootc it's running emulated with the target arch, so this check will pass)

[jmarrero]

lgtm