feat(consts/exit-codes): add exit codes enum

[JuanGalilea]

why? thread about a convention for failing actors due to an invalid input

After a talk with @B4nan we came to a conclusion that an enum here would be good enough for some ergonomics around this, so it can be used as:

await Actor.exit("your input sucks", { exitCode: ACTOR_EXIT_CODE.INVALID_INPUT });