Add DistroContext.install(). It takes a tar file containing secrets, decrypts it, and installs all secrets needed on target and present in that file. For every file that should be extracted, it logs if it acutally did something or didn't.
It also features an only_missing argument, which is just a stub for "allow to define somy extraction policy with respect to replacing all / some / not replace / whatever. Not thought through.
Signed-off-by: Jan Lindemann <jan@janware.com>