docs: Generate API reference using sphinx-autoapi

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

Use the sphinx-autoapi plugin to generate API reference documentation. The configuration is based on https://github.com/ni/measurement-plugin-python/blob/main/packages/service/_docs_source/conf.py

Why should this Pull Request be merged?

Closes AB#3111356 - Enable doc generation with sphinx-autoapi

What testing has been done?

Ran poetry run sphinx-build docs docs/_build -b html -W --keep-going locally and examined docs\_build\index.html in a web browser.

[github-actions]

Test Results

   10 files  ±  0     10 suites  ±0   26s ⏱️ +4s
  391 tests + 41    386 ✅ + 42   5 💤  -  1  0 ❌ ±0 
3 910 runs  +410  3 860 ✅ +420  50 💤  - 10  0 ❌ ±0 

Results for commit 00ca56c. ± Comparison against base commit 0d515bc.

♻️ This comment has been updated with latest results.

[bkeryan]

The output is uploaded as a build artifact:

Once we have a ReadTheDocs site for this project, the output will be hosted on the RTD site and we won't need this build artifact.

[bkeryan]

FYI: The "Run CI / Check / Check nitypes" check is pending because I renamed it and the branch protection rules reference the old name. I will update the branch protection rules before merging this PR.