Add autopkgtests to john's packaging

Add autopkgtest to check for correct functioning of the package. debian/test/smoke performs a simple smoke test, debian/test/crack-from-stdin takes a wordlist from stdin and recovers the hashes of various hash algorithms, lastly debian/crack-crypt-from-wordlist takes the default wordlist to recover hashes in crypt format. Rule-based- and bruteforce-approaches are not tested due to their load. Furthermore, bcrypt hashes are omitteds, since they are not supported on bullseye anymore.

debian/tests/helper/ contains a shell script used to generate the test data.