Implement client-side APK discovery in `apko` #2124

Job	Run time
annotations	30s
build-all-examples-amd64 (ubuntu-latest)	57s
build-all-examples-amd64 (macos-latest)	58s
build-date-epoch	1m 0s
source-date-epoch	59s
build-nginx-multiarch	35s
build-nginx-all-arches (x86_64)	32s
build-nginx-all-arches (386)	30s
build-nginx-all-arches (armv7)	26s
build-nginx-all-arches (aarch64)	33s
build-nginx-all-arches (riscv64)	27s
build-nginx-all-arches (s390x)	32s
build-nginx-all-arches (ppc64le)	26s
	8m 25s

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