Decrease runtime of lint job

[angela97lin]

#2670 introduced pydocstyle and darglint packages. The darglint package specifically increases the runtime of our lint job by a few minutes. While we were okay with this addition, I suspect that there's a way to cut down on this time. Some suggestions are:

• Find a way to only lint the changed files. @freddyaboulton mentioned that scikit-learn has a way to do so via bash script that might be worth exploring: Docstring formatting and linting using pydocstyle and darglint #2670 (comment)
• Explore github pre-commit hooks, and only call the lint job on files modified (that are not test files, and .py files).

[dsherry]

Thanks for filing! Please use the "spike" label instead of "[SPIKE]" title prefix