* packaging: Use cargo-deb multiarch support
This allows building all platforms from one definition,
assuming the --multiarch=foreign flag is used.
* packaging: Use correct path naming for unixd service files
While cargo-deb works around the mistake, better to name them as per the
rules: https://github.com/kornelski/cargo-deb/blob/main/systemd.md#systemd-unit-file-naming
* docs: Update book chapter on Debian packaging
* packaging: Shift Debian builds to a separate build profile
* packaging: Add deb for kanidmd
