Document unhealthy annotation

[lentzi90]

Add a section under Cluster-api-provider-metal3 for unhealthy annotation. Mention also that the annotation is automatically applied when remediation times out.

The user guide code can be found here.

[lentzi90]

/good-first-issue /triage accepted

[metal3-io-bot]

@lentzi90: This request has been marked as suitable for new contributors.

Please ensure the request meets the requirements listed here.

If this request no longer meets these requirements, the label can be removed by commenting with the /remove-good-first-issue command.

In response to [this](https://github.com/metal3-io/metal3-docs/issues/403): >/good-first-issue >/triage accepted Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[metal3-io-bot]

Issues go stale after 90d of inactivity. Mark the issue as fresh with /remove-lifecycle stale. Stale issues will close after an additional 30d of inactivity.

If this issue is safe to close now please do so with /close.

/lifecycle stale

[Rozzii]

/remove-lifecycle stale

[Rozzii]

/remove-lifecycle stale

[metal3-io-bot]

Issues go stale after 90d of inactivity. Mark the issue as fresh with /remove-lifecycle stale. Stale issues will close after an additional 30d of inactivity.

If this issue is safe to close now please do so with /close.

/lifecycle stale

[Rozzii]

/remove-lifecycle stale

[Rozzii]

/lifecycle frozen