Show izanami's environment variables on load.

Show all the configuration variables from the enviroment when running
one of the izanami's bins. The info is shown in the standard output.

Example:

    $ IZANAMI_AUTH=disable IZANAMI_SANDBOX=/path/to/recipes izanami app
    == Running izanami-app
    == Environment configuration:
    >> IZANAMI_SANDBOX=/path/to/recipes
    >> IZANAMI_AUTH=disable
    ...

This is useful for debugging and logging.