Add filter to check validity of CITATION.cff followup

[jspaaks]

Description

Took another stab at #4 based off @fdiblen 's earlier PR #47 . Resulting set of URLs is the same as what @abelsiqueira showed earlier, but with code I can understand more easily.

Related issues:

• 4

Instructions to review the pull request

• Make a GitHub Access token here https://github.com/settings/tokens
  • Make sure you copy it when it appears on screen, because you can't see it again. You can reset it, though.
• export GITHUB_TOKEN as an environment variable with the token above
• install Node >= 14

• cd $(mktemp -d --tmpdir cffbot-XXXXXX)
  git clone https://github.com/cffbots/filtering .
  git checkout <this-branch>
  npm install
  node query.mjs

[jspaaks]

conflicts resolved, thanks for the review Abel