Support `Any` as input

[bfirsh]

I want it to be possible to start with the simplest, most flexible thing, then layer in things on top.

You should be able to start with this:

def predict(name):
    return f"hello {name}"

Then, you can augment it. If you want to get some fancy output, add an output type. If you want a better form field and some validation, add an input type. If you need some setup processing, add a Predictor and a setup() function.

See also

• Feature request: Allow a type for cog.Input to be any cog.BaseModel #470
• Make output type optional #1312

[bfirsh]

Implementation: #968

[bfirsh]

There are some failing tests in here representing the behavior: #1313

[bfirsh]

From #538:

My dream is arbitrary JSON encodable types in/out as the lowest level thing, then more specific types built on top of that. We've got that for outputs, but not inputs yet. :D