cli as an alternative to pangeo-forge-runner

[keewis]

Currently there is one official way to run recipes: pangeo-forge-runner. As this is pretty hard to use (lots of magic and issues like the one pangeo-forge/pangeo-forge-runner#168 is trying to solve), the ad-hoc way of running recipes appears to be to execute recipe files as scripts, which is not ideal because it couples infrastructure and transformation code.

To work around this, I've tried to sketch out a cli that:

• requires recipes to be functions that take the pipeline as a parameter
• instantiates the runner and pipeline from a runtime config file
• allows passing additional runtime parameters to the function

(but this still needs a lot of work to make things consistent and without surprises)

I've also tried to add a command that creates a skeleton recipe, somewhat like what maturin init does, but this does not work at all, at the moment.

@norlandrhagen, this is the draft I showed you during the meeting this week.