apk: define arch=source qualifier

[gernot-h]

This proposes a similar approach for Alpine to what we agreed on for Debian in #57.

Thanks for reviewing, let me know what you think and if you need an additional issue for it!

[gernot-h]

@Foxboron, as you contributed apk, I would also be interested in your opinion.

[Foxboron]

I've read the Debian discussion and I don't think I agree with lamby and would prefer having a src qualifier to go along with pkg, but considering this was decided in 2021 I don't think my opinion matters on this.

Generally I think overloading the arch field is a mistake that is making this spec complicated.

[gernot-h]

Thanks, @Foxboron, for your opinion! Apart from the how we express this, you agree that it actually makes sense if we define a way to specify package sources and also use abuild srcpkg as reference, right?

[Foxboron]

Apart from the how we express this, you agree that it actually makes sense if we define a way to specify package sources and also use abuild srcpkg as reference, right?

Yes