[Downloader] max_python_version key in cog info.json

### What component of Red (cog, command, API) would you like to see improvements on?

Downloader

### Describe the enhancement you're suggesting.

Similar to the `min_python_version` key (#1452, #1455), it would be great to have a similar key for the maximum version for the (albeit rare) deprecations/removals between minor Python versions.

I am imagining this would mirror the behaviour of the `max_bot_version` key - only impacting installations and updates of the cog through Downloader.

### Anything else?

I would be happy to take this on if approved, and note to me/whoever does this: make sure to update the docs & info.json schema, as well as the code