Cut CI time/network by caching go build/vet/test artifacts in S3.
- bump build/test/pre-commit/release(test,build) to
artifactapi.../gobuilder:0.1.2-alma9
- wire GOCACHEPROG via go-cache-plugin with an absolute cache dir
- add GOCACHE_* env (ci-tomswall prefix) and AWS creds from org secrets
- leave rpm package/upload steps untouched (no Go toolchain)