Add examples for pip and poetry

[tyler-yankee]

This addresses #266 by adding two new examples for usage of Drake's Python API:

• installing Drake by creating a virtual environment and pip install drake
• installing Drake by creating a poetry project and poetry add drake

Both examples use the Python version of the particle demo found in other examples, and both have CI through GitHub Actions only. The poetry example's GHA script has a separate setup script for Mac because the installation of pipx, which is used to install poetry, is a bit different than on Ubuntu.

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