Add a [reusable] workflow for building wheels

[peytondmurray]

This PR adds a workflow for building wheels. The workflow is triggered when

1. A PR is made; PRs which break wheel builds will fail
2. A release is made; if a release is made, the wheels are built and then uploaded to PyPI automatically. This requires trusted publishing to be set up in the repository. Please feel free to reach out if you need help with this, I'm happy to help set this up!
3. Whenever the workflow is manually triggered, in which case it will also upload to PyPI automatically.

[peytondmurray]

@aktech Would appreciate your input, particularly on the part that triggers the reusable workflow.

[aktech]

Looks good to me other than some minor nitpicks.

Also, I am guessing the extra files like bazel-* and wheel is committed accidentally.

[peytondmurray]

Also, I am guessing the extra files like bazel-* and wheel is committed accidentally.

Ugh, yes, these are added to a .gitignore in #40. I've removed these files here in this PR now.

[agriyakhetarpal]

Hi! I stumbled across this PR via the same issue as the one linked in the code comment here, and I thought it would be nice to suggest a few improvements that I was able to notice. I had a chat with @peytondmurray beforehand so that this doesn't become an unsolicited review :D

[agriyakhetarpal]

All good from my side and I'm happy I was able to help somewhat!

[peytondmurray]

@hassler-google Is there anything else we need to do here? If not, could you please approve the workflow, then merge?