feat(renovate): add Gitea update automation

Run Renovate in Kubernetes to create reviewed image update PRs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

renovate/k8s/secrets.yaml.example

@@ -0,0 +1,11 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: renovate-secrets
+  namespace: renovate
+type: Opaque
+stringData:
+  RENOVATE_TOKEN: ""
+  RENOVATE_ENDPOINT: "https://gitea.forust.xyz/api/v1"
+  RENOVATE_REPOSITORIES: "forust/homelab"
+  RENOVATE_GITHUB_COM_TOKEN: ""