* ci: build and test using 1.18 and 1.19 (drop 1.17)
* remove pre-1.18 compat code, update README
* go install goimports before checkout
* update chainguard-dev/actions to versions that go install
* Support --tag and --tag-only with nop publisher
* log the output, for debugging
* unset KO_DOCKER_REPO for push=false test
* run e2e test first before other stuff
* review feedback