Add notice to README

[elastisys-staffan]

Warning

This is a public repository, ensure not to disclose:

• personal data beyond what is necessary for interacting with this pull request, nor
• business confidential information, such as customer names.

What kind of PR is this?

Required: Mark one of the following that is applicable:

• kind/feature
• kind/improvement
• kind/deprecation
• kind/documentation
• kind/clean-up
• kind/bug
• kind/other

Optional: Mark one or more of the following that are applicable:

Important

Breaking changes should be marked kind/admin-change or kind/dev-change depending on type
Critical security fixes should be marked with kind/security

• kind/admin-change
• kind/dev-change
• kind/security
• [kind/adr](set-me)

What does this PR do / why do we need this PR?

Adds a notice to the README.

Also back-ports necessary commits to fix broken CI.

• Fixes https://github.com/elastisys/ck8s-issue-tracker/issues/732

Information to reviewers

Checklist

• Proper commit message prefix on all commits
• Change checks:
  • The change is transparent
  • The change is disruptive
  • The change requires no migration steps
  • The change requires migration steps
  • The change updates CRDs
  • The change updates the config and the schema
• Documentation checks:
  • The public documentation required no updates
  • The public documentation required an update - [link to change](set-me)
• Metrics checks:
  • The metrics are still exposed and present in Grafana after the change
  • The metrics names didn't change (Grafana dashboards and Prometheus alerts required no updates)
  • The metrics names did change (Grafana dashboards and Prometheus alerts required an update)
• Logs checks:
  • The logs do not show any errors after the change
• PodSecurityPolicy checks:
  • Any changed Pod is covered by Kubernetes Pod Security Standards
  • Any changed Pod is covered by Gatekeeper Pod Security Policies
  • The change does not cause any Pods to be blocked by Pod Security Standards or Policies
• NetworkPolicy checks:
  • Any changed Pod is covered by Network Policies
  • The change does not cause any dropped packets in the NetworkPolicy Dashboard
• Audit checks:
  • The change does not cause any unnecessary Kubernetes audit events
  • The change requires changes to Kubernetes audit policy
• Falco checks:
  • The change does not cause any alerts to be generated by Falco
• Bug checks:
  • The bug fix is covered by regression tests

[cristiklein]

Short and sweet, thanks!

[elastisys-staffan]

Had a quick chat with @pettersv, we will wait with merging this until AM/commercial is done with their messaging. Will convert this PR to draft in the meantime.

[pettersv]

LGTM!