docs: document machine-id workaround for containerd-based Kubernetes clusters

[markphelps]

Problem

Users deploying Flipt Pro on containerd-based Kubernetes clusters (GKE, modern EKS) encounter a license validation error because the container cannot determine a machine ID:

license is invalid; additional features are disabled. {"error": "machineid: machineid: no machine-id found"}

This happens because the machineid library relies on /etc/machine-id, dbus, or Docker-specific cgroup/mountinfo paths — none of which exist in containerd-based environments.

Proposed Documentation

Add a troubleshooting section to the licensing docs (v2/configuration/licensing.mdx) and/or the Kubernetes deployment guide (v2/guides/operations/deployment/deploy-to-kubernetes.mdx) covering:

1. Workaround: Mount host machine-id

# In Helm values.yaml
extraVolumeMounts:
  - name: machine-id
    mountPath: /etc/machine-id
    readOnly: true

extraVolumes:
  - name: machine-id
    hostPath:
      path: /etc/machine-id

2. When the code fix lands (flipt-io/flipt#5426)

Document the FLIPT_MACHINE_ID environment variable / license.machine_id config option as the preferred approach for container environments.

Affected Environments

• GKE (containerd)
• EKS with containerd
• Any Kubernetes cluster not using Docker as the container runtime
• Rootless containers
• Serverless container runtimes (Fargate, Cloud Run)

Related

• feat: support configurable machine fingerprint for license validation in containers flipt#5426 — configurable machine fingerprint
• feat(flipt-v2): add hostPath mount option for /etc/machine-id helm-charts#270 — hostPath mount option in Helm chart