Mount Docker socket into job containers for docker build

Job containers need access to the DinD daemon for docker build/push.
Mount /var/run/docker.sock from DinD into job containers and set
docker_host in runner config.

infra/kubernetes/platform/gitea-runner/runner-config.yaml

@@ -11,6 +11,8 @@ data:
       capacity: 1
       timeout: 1h
     container:
-      options: "-v pnpm-store:/pnpm-store -e PNPM_STORE_DIR=/pnpm-store -e COREPACK_HOME=/pnpm-store/.corepack"
+      options: "-v pnpm-store:/pnpm-store -v /var/run/docker.sock:/var/run/docker.sock"
+      docker_host: tcp://localhost:2375
       valid_volumes:
         - "pnpm-store"
+        - "/var/run/docker.sock"