CMD variable should support different formats

[kbdharun]

The CMD command in Dockerfile syntax supports shell format (i.e. CMD command param1 param2), exec form and also ENTRYPOINT like format (i.e. CMD ["param1","param2"]); currently vib only supports the shell format and it parses it as /bin/sh -c ./command param1 param2 instead of Docker's normal ./command param1 param2.

IMO we should implement it as an ENTRYPOINT like format, i.e. CMD ["param1","param2"])` which can be passed along with an "entrypoint" variable in the recipe which points to the commands binary.

Also, When an "entrypoint" variable isn't defined in the recipe, the "cmd"'s definition should be interpreted as CMD ["executable","param1","param2"] (exec form) [This would work the best for most of our use cases]

Ref. https://github.com/Vanilla-OS/Vib/blob/main/api/structs.go and https://docs.docker.com/reference/dockerfile/#cmd