Adds %ai error magic command to explain the most recent error

[JasonWeill]

Adds a new %ai error command that explains the most recent error in the current notebook using the chosen model. Updates the documentation to mention this new magic command. Fixes #62.

[JasonWeill]

This is updated to incorporate the click logic from #188.

[3coins]

@JasonWeill
Rebasing from main and submitting again should fix the CI.

[3coins]

@JasonWeill
I tested the magic and it works great. Some minor things I noticed in the example notebook:

1. One of the outputs bleeded into the next cell. Is this expected?
   
2. While running the example, I had to set the env variables for the chatgpt provider, so had to add an additional cell. This misaligned the references for cell numbers in the subsequent cells and caused an error on last cell. Wondering if we should add a placeholder cell for setting the api key.

[JasonWeill]

1. In the screen shot, the selected cell is a Markdown cell, not a continuation of the output. This shows a bug with the cell toolbar; see Cell toolbar overlaps horizontal rule in markdown cell jupyterlab#14646
2. I typically set env variables before starting JupyterLab; I try to avoid setting them in the example files, to minimize the chance of me accidentally checking an API key in.