Add a function 'environment' generator

[dknutsen]

Add a generator or utility function that will add an 'environment' to a function. This should do the following:

• read the function config (if it exists, if not abort)
• add an environments array to the function config if not already there, then add the environment to it
• overwrite the function config with the new and improved Hash
• create a .env file in the function source dir with the env name templated in