Save incremental progress on issue / PR fetch failures

This commit implements logic for saving incremental progress when
encountering an error fetching issues or PRs (such as an unsupported
even type). When encountering such an error, keep fetching other
issues and store the failed issue / PR IDs in the state file. The
current run exit with an error code of `EXIT_API_ERROR` (3).
Subsequent runs will then retry fetching these failed resources.

Author: lschuermann