Add Doc Linting to CI

[kidrahahjo]

Description

We are using pydocstyle to check that our document strings are in the numpy docstring style. The configuration for pydocstyle is in setup.cfg. I chose flow/utils/template_filters.py as the first file for testing this, feel free to suggest another file if you think there is a better candidate

Motivation and Context

Replicates glotzerlab/signac#294 for signac-flow
Fixes glotzerlab/signac-flow#276

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change¹

¹The change breaks (or has the potential to break) existing functionality.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• My code follows the code style guideline of this project.
• The changes introduced by this pull request are covered by existing or newly introduced tests.

If necessary:

• I have updated the API documentation as part of the package doc-strings.
• I have created a separate pull request to update the framework documentation on signac-docs and linked it here.
• I have updated the changelog.

[kidrahahjo]

I guess the pre-test-checks test won't fail because flow/utils/template_filters.py is documented according to the numpy docstring style.

[vyasr]

If you look at the pydocstyle documentation, you'll see that it autodetects the style of docstrings. So for now it's working by detecting our current style, but as docstrings change to numpy style it should automatically detect that and switch. It's not immediately clear from the documentation if it detects on a per-docstring, per-file, or per-project level. It suggests that it's per-docstring, but we'll have to figure that out as we go along. As @CryoZEUS starts converting files we can start testing them by whitelisting the appropriate files.

[vyasr]

@klywang I'm going to go ahead and merge this PR since it's a pretty small one.