feat: add maintainer drift detection feature

[ahmadqasembader]

I introduced a maintainer-list drift detection. It compares the org repos governance files against the maintainers.yml file in .project, the detection works on every push or PR, in this case, if a drift is detected, a warning will be issued.

The second part is a scheduled GitHub Actions that runs every 1st of the month, which tries to validate the maintainers again and open a PR if any drift was detected

[jeefy]

This is a more complicated feature. Maintainers are considered people who "speak for the project" and are designated through a project's governance model. Drift through PRs isn't a correct method to do this.

Instead, one idea was to ping projects if a maintainer.yaml hasn't been updated in six months (via an issue) asking "is this still up to date? Also (if applicable) we see these $x people have been contributing heavily over the last six months and these $y people haven't touched anything in GitHub in the last six months"

[ahmadqasembader]

@jeefy, the drift detector has been refactored and introduced a health-check-and-report feature as suggested.

The scheduled workflow will check the maintainers.yml and whether it has not been edited for the last 6 months.

If yes, we will create an issue and tag the first 3 owners or the top 3 contributors of the Org.

An example of the Issue that will be created:

Maintainer List Health Check — kubernetes

Hi X 👋

maintainers.yaml has not been updated in 194 days (threshold: 180 days).
Please confirm the list below still reflects your project's governance model.

🕒 Checked: 2026-04-29 08:00 UTC
📅 Activity window: last 6 months

Current Maintainers — Activity

Maintainer	Commits	Merged PRs	Active repos	Last seen
@thockin	312	71	kubernetes, api, apimachinery +9 more	2026-04-29
@liggitt	278	64	kubernetes, apiserver, client-go +4 more	2026-04-28
@derekwaynecarr	143	38	kubernetes, component-base, api	2026-04-22
@dims	89	22	kubernetes, apimachinery, api	2026-03-15
@smarterclayton	14	3	apiserver	2026-01-20
@lavalamp	3	0	kubernetes	2025-11-04
@wojtek-t	0	0	—	—

Active Contributors Not Yet in Maintainer List

These contributors have been active across project repos in the last 6 months but do not appear in maintainers.yaml. Consider whether any should be nominated per your governance process.

Handle	Commits	Merged PRs	Active repos
@bentheelder	104	28	kubernetes, client-go, api +1 more
@pohly	91	21	apiserver, kubernetes
@jpbetz	77	18	apiserver, apimachinery
@alexzielenski	55	14	apiserver, api
@gnufied	43	9	kubernetes, component-base

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No changes are required automatically. Please update maintainers.yaml if this no longer reflects your governance, or close this issue to confirm it is still accurate. This issue was opened by cncf/automation maintainer health-check tooling.