Add scripts for type-checking rst doc files and Jupyter notebooks

[jas-ho]

Description

Here are two scripts I used for checking for type errors in documentation and notebooks. I don't know whether this is of use to anyone. So I figured I'll open a PR and see..

Limitations

There are currently some false positives from documentation code blocks which contain ellipses like # instantiate your policy here. Just ignore these or fix them in case you'd like to include these scripts in CI.

Testing

Manually introducing type errors and running the scripts.

[AdamGleave]

This feature seems useful, but I'm worried about maintenance burden of an extra script. @ernestum what do you think? https://github.com/nbQA-dev/nbQA looks like it can run mypy on notebooks so that might be one more maintainable way of getting some type checking, but that wouldn't solve the rst doc file problem. EDIT: I see this is actually using nbqa, I think we can probably simplify that Python script using it, might be easier as a shell script.