Allow setting default env files locations

[squivix]

I want to be able to permentantly set the default location to search for env files if it's not specified in the command.
Right now it's a constant:

env-cmd/src/get-env-vars.ts

Line 6 in 8f35b71

const ENV_FILE_DEFAULT_LOCATIONS = ['./.env', './.env.js', './.env.json']

But I want to set it in some sort of config, possibly through the package.json file:

  "env-cmd": {
    "ENV_FILE_DEFAULT_LOCATIONS": ["./env/*.env"]
  }