Speed up nightly builds (#27045)

* Rootless/ful docker images build separately
* Vendor go modules outside docker to speed up the build

Thanks to Alex Ellis for these suggestions (and actuated runner build
time)

.github/actionlint.yaml

@@ -0,0 +1,4 @@
+self-hosted-runner:
+  labels:
+    - actuated-4cpu-8gb
+    - actuated-4cpu-16gb