added filter to check that repo has more than a handful PRs

[jspaaks]

Description

This PR adds a filter to exclude repositories that have fewer than 5 Pull Requests (open + closed). The filter does not account for pagination of API results yet (because we don't need it for our purposes). I did include a warning that triggers when paginated results will affect the filtering.

Related issues:

• 6

Instructions to review the pull request

• Make a GitHub Access token here https://github.com/settings/tokens
• cp secrets.txt.example secrets.txt
• Update the value of GITHUB_TOKEN in secrets.txt
• install Node >= 14
• npm install

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

[jspaaks]

Marked draft until some of the other PRs have been merged, there will be conflicts.

[jspaaks]

Thanks for reviewing!