ci: move Go steps to gobuilder, enable S3 build cache

Standardizes on the estate gobuilder image for every step invoking
the Go toolchain and wires in the shared S3-backed GOCACHEPROG.

- Replace golang:1.25 and almalinux9-gobuilder:20260606 with
  gobuilder:0.1.2-alma9 in build/test/pre-commit/release(build)
- Add GOCACHE_* env + AWS creds from org secrets to those steps
- Bump their k8s resource requests/limits for compile+cache overhead

.woodpecker/release.yml

@@ -30,7 +30,7 @@ steps:
             cpu: 2
 
   - name: package
-    image: artifactapi.k8s.syd1.au.unkin.net/docker-internal/rpmbuilder:0.1.0-alma9
+    image: git.unkin.net/unkin/almalinux9-rpmbuilder:latest
     commands:
       - ./scripts/build-rpm.sh ${CI_COMMIT_TAG}
     depends_on: [build]