Fix docs pipeline, make docs tests easier to run locally and on different OSes

[wren]

While making PR #1553, I noticed that the docs pipeline is failing. So, this PR:

• Fixes the docs pipeline
• Removes dependency on yq package (since it uses jq, which might not be installed)
• Uses xmltodict to read sitemap
• Makes task runner poe work better on other systems (like Windows) by creating OS-agnostic tasks (in the newly created tasks.py file in the root)
• Removes dependency on curl which isn't reliably installed on contributors' machines
• Updates linting/testing to go over new tasks.py file to reduce future errors in tasks
• Update docs pipeline to use poe tasks
• Adds package.json and package.lock files since we already use npm to test the docs site, anyway. This stops us from hardcoding the dependencies into the CI pipeline, and makes it easier to get everything you need locally for testing the docs site (just run npm install).
• Having our dependencies in a proper package.json file will also allow Dependabot to test and notify us of updates/issues

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.