Generate and publish Python API docs

[ScottTodd]

(Issue migrated from nod-ai/SHARK-ModelDev#106)

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Users would find it helpful to view API documentation pages instead of just needing to read through source files, samples, and tests. I would also like to link to API docs from https://iree.dev/guides/ml-frameworks/pytorch/.

IREE Python used readthedocs (with mixed results): https://iree-python-api.readthedocs.io/en/latest/

• I also evaluated mkdocstrings for integrated into IREE's mkdocs website, but it was awkward: Generate and publish API reference pages iree#5477 (comment)

Could see what PyTorch uses for https://pytorch.org/docs/stable/index.html (sample page: torch.nn.Linear)

Even if we don't end up publishing API docs, going through and adding docstrings and help text could still be useful.