This commit adds support for providing custom CA certificates
during the build process. It allows a user to specify one ore
more CA file(s) via the new <certificates> section and/or
via the command line. The certificate files will be imported
directly after the image bootstrap has finished (where the
required CA update tools are available), but before any
further packages are retrieved, solving for situations where
the chroot environment needs certificates, e.g. when there's
a proxy server in the build environment.
Co-authored-by: Marcus Schaefer <marcus.schaefer@gmail.com>