:book: Document the change of instanceID in v1beta1

[pierreprinetti]

What this PR does / why we need it:

This docs patch adds mention of the change to OpenStackMachine.spec.instanceID that moves to status in v1beta1 (see https://github.com/kubernetes-sigs/cluster-api-provider-openstack/pull/1988).

TODOs:

• [x] squashed commits
• if necessary:
  • [ ] includes documentation
  • [ ] adds unit tests

/hold

[netlify[bot]]

✅ Deploy Preview for kubernetes-sigs-cluster-api-openstack ready!

Name	Link
🔨 Latest commit	fe80a3f3babe51b4047895038c093e27d30e9303
🔍 Latest deploy log	https://app.netlify.com/sites/kubernetes-sigs-cluster-api-openstack/deploys/660fb239cce612000833bf5f
😎 Deploy Preview	https://deploy-preview-2003--kubernetes-sigs-cluster-api-openstack.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[huxcrux]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lentzi90, pierreprinetti

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubernetes-sigs/cluster-api-provider-openstack/blob/main/OWNERS)~~ [lentzi90] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[dulek]

/hold cancel

Let's get this merged, thanks @pierreprinetti!