add an annotate_list method

[zingale]

PR Summary

The annotate_clear() method takes an optional index of the annotation to remove, but there
is not high-level method to see the indices of the currently applied annotations. This PR adds
an annotate_list() method that simply prints the annotations and their indices.

PR Checklist

• Code passes flake8 checker
• New features are documented, with docstrings and narrative docs
• Adds a test for any bugs fixed. Adds tests for new features.

[zingale]

Note: I also fixed a sphinx error in the annotate_clear title ~ length.

[munkm]

Since you've added a new callback, can you add it to the api reference for the list of callbacks at doc/source/reference/api/api.rst too, so that the api reference is generated too?

Thanks for this feature! I think it'll be really useful!

[munkm]

Ok, I see that you're matching the annotate_clear method in the way that this operates on all annotations. That said, I'm wondering if it's maybe clearer to name it something like list_annotations? I feel like that might be more intuitive when looking through different operations one could do on a plot. If I were casually using yt, I'd think that annotate_list would be a specific annotation of a list object, just like annotate_scale annotates a scale.

[zingale]

I agree, it would be clearer, and I'm happy to change the name, but I was trying to match the convention already in place. E.g., clear_annotations() would also be more clear than annotations_clear()

[zingale]

because of some fork problems on my end, I will close and reissue this PR. Sorry :(