Paginate CircleCI API v2 list endpoints and handle 429 rate limits

Documented steps

1. Make the initial GET request to any paginated list endpoint (e.g. GET https://circleci.com/api/v2/project/{project-slug}/pipeline) with header 'Circle-Token: $CIRCLE_TOKEN'.
2. Read the 'next_page_token' field from the JSON response; it is a string when more pages remain and null on the final page.
3. If next_page_token is not null, repeat the same GET request adding the query parameter page-token={next_page_token value}.
4. Continue looping until a response's next_page_token is null, then stop.
5. If any response returns HTTP 429, read the 'Retry-After' header (seconds to wait) before retrying rather than retrying immediately.
6. Inspect 'RateLimit-Remaining'/'RateLimit-Reset' (or the legacy 'X-RateLimit-*' variants) response headers to back off proactively before hitting 429.
7. Reference: https://circleci.com/docs/guides/toolkit/api-developers-guide/