Enable setting of cli options with environment variables

[LMH01]

I think that it would be a good idea to add the possibility that cli options can be defined using environment varibles in addition to providing them when the program is run.
This would allow the possibility to specify the arguments --allowed-instruction-file and --memory-config-file once in a .env file instead of needing to provide them to the program on each run.

This can be done by using the env feature of clap so implementation is basically trivial.