Build replacement ABI packages before building requested packages

[kwitaszczyk]

Pure-capability ABI builds require replacement packages (hybrid ABI on Morello; host's ABI on other architectures). poudriere-infrastructure should automate the process of preparing such packages, instead of requiring a user to manually build them and upload them to pkg.cheribsd.org.

overlay/rootfs/{arm64,amd64} should be applied to a rootfs of a Poudriere jail for replacement packages. When using ZFS, it is important to remember to re-create a @clean snapshot that is automatically created by poudriere jail -c.