Limit the number of results to be actioned per run

Sometimes a triage rule will detect thousands of issuables to action. This might be too many notifications for a maintainer to handle.

This is a proposal to only action a subset of the detected issuables in the current run. The remaining issuables could be part of the next run.

conditions:
  limit:
    limit: first
    threshold: 100

conditions:
  limit:
    limit: last
    threshold: 50