Use custom runner image with jq, kustomize, docker pre-installed

Build a runner-image based on node:20-bookworm with all CI tools
baked in, avoiding apt-get install in every workflow run. Runner
labels now point to gitea.coreworlds.io/lazorgurl/runner-image.

.gitea/workflows/ci.yaml

@@ -20,8 +20,6 @@ jobs:
         with:
           fetch-depth: 0
 
-      - run: apt-get update && apt-get install -y jq
-
       - name: Detect changed apps
         id: filter
         run: |