Extend the check command to be able to use files as a source for their allowlist or blocklist.

Currently, this is possible by passing a flag multiple times:

# Allow both MIT and GPL exclusively
./vendor/bin/composer-license-checker -a MIT -a GPL ...

# Deny both BSD and Unlicense
./vendor/bin/composer-license-checker -b BSD -b Unlicense ...

An example where this could be used is in shopware/platform: they have extracted their allowed licenses into an .allowed-licenses file and need to use sed to parse the file into command line arguments.