[Feature Proposal] - Add PyPI publishing workflow for Python SDK

[hiromesh]

Follow-up from #4496 . Add a publish.sh script and CI workflow to publish the Python SDK to PyPI on release.

[markmandel]

Now we're out of Google, there's likely work we can do to automate all our package publishing. A broader project though.

[igooch]

@shrutiyam-glitch