[Enhancement] Add support for a "twin" configuration option that pairs with command line option --include

[nagmat84]

Most command line options also have a corresponding configuration option which can be used in dracut.conf. (For example, --install=<file> becomes install_items=" <file>", etc.). The command line option --include <src> <dst> allows to embed a file into the Initramfs at another location than on the original filesystem.

However there is no configuration option for that. This enhancement asks for adding such an configuration option which mirrors the behavior of the --include command line option.

Why it is important: If one relies on automatic kernel updates, the call chain it usually something like running the update command of your package manager, which in turn calls make all && make modules_install && make install inside the kernel source directory, make install in turn calls the script installkernel, which under the hood calls dracut. Along this chain, there is no option to pass any extra command line options to dracut, unless of course you are willing to patch any of those scripts, but this interferes with any automatic update of those scripts again. Hence, everything dracut has to do, must be configured via the configuration files inside /etc/dracut.conf.d/.