Add generic build manifest #93

Job	Run time
prepare	6s
build (aarch64, httpreply, fc) / buildunikernel	1s
build (x86_64, httpreply, fc) / buildunikernel	8m 23s
build (aarch64, httpreply, qemu) / buildunikernel	56s
build (x86_64, httpreply, qemu) / buildunikernel	1s
buildgeneric (aarch64, httpreply-go) / buildapp	1m 10s
buildgeneric (x86_64, httpreply-go) / buildapp	1m 12s
build (aarch64, httpreply, qemu) / buildimage	23s
buildgeneric (aarch64, httpreply-go) / sign	18s
buildgeneric (x86_64, httpreply-go) / sign	18s
build (aarch64, httpreply, qemu) / sign	16s
manifestgeneric (httpreply, go) / manifest	17s
build (x86_64, httpreply, qemu) / buildimage	1s
build (x86_64, httpreply, fc) / buildimage	1s
build (aarch64, httpreply, fc) / buildimage	1s
build (x86_64, httpreply, qemu) / sign	1s
build (x86_64, httpreply, fc) / sign	1s
build (aarch64, httpreply, fc) / sign	1s
manifest	1s
	13m 28s

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