ci: add Mergify configuration

[leseb]

Summary

• Add .github/mergify.yml with rules for:
  • Ping author on conflicts and add needs-rebase label
  • Auto-remove needs-rebase label when conflict is resolved
  • Auto-update PRs that are 3+ commits behind main

Test Plan

• Verify Mergify picks up the config after merge

Signed-off-by: Sébastien Han seb@redhat.com
Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com

[leseb]

we need to enable mergify

[franciscojavierarceo]

I spent a little time with my clanker on this and here's a suggested setup:

pull_request_rules:
  - name: add needs-rebase label on conflicts
    conditions:
      - conflict
      - -closed
    actions:
      label:
        add:
          - needs-rebase

  - name: remove needs-rebase label when conflict is resolved
    conditions:
      - -conflict
      - -closed
    actions:
      label:
        remove:
          - needs-rebase

queue_rules:
  - name: default
    queue_conditions:
      - base=main
      - -draft
      - -conflict
      - "#approved-reviews-by>=1"
      - check-success=ci
    merge_conditions:
      - check-success=ci

priority_rules:
  - name: hotfix PRs go first
    conditions:
      - label=hotfix
    priority: high

  - name: high-priority PRs go ahead of normal PRs
    conditions:
      - label=high-priority
    priority: medium

And I believe we can use @mergifyio queue and @mergifyio dequeue, and we can add the hotfix or high-priority label when appropriate.

This also reduces all of the noise IMO.