Add old kubernets docs

docs/kubernetes/apps/nextcloud.md

docs/kubernetes/apps/smtp.md

docs/kubernetes/cert-manager.md

docs/kubernetes/cronjobs.md

docs/kubernetes/databases/postgresql.md

docs/kubernetes/development.md

docs/kubernetes/dns.md

docs/kubernetes/events.md

docs/kubernetes/external-secrets.md

docs/kubernetes/gke.md

docs/kubernetes/helm/documentation.md

docs/kubernetes/helm/publishing.md

docs/kubernetes/helm/testing.md

docs/kubernetes/iam.md

docs/kubernetes/ingress/ingress.md

docs/kubernetes/k3s.md

docs/kubernetes/k9s.md

docs/kubernetes/kind.md

docs/kubernetes/kubernetes.md

docs/kubernetes/lens.md