Provide template for target binary name in Dockerfile generator

[mgencur]

Some upstream tests from Serving depend on exact path that is compatible with binaries generated by ko. Examples: https://github.com/knative/serving/blob/main/test/conformance/runtime/cmd_args_test.go#L43 https://github.com/knative/serving/blob/main/test/conformance/runtime/readiness_probe_test.go#L98

This is required to onboard Serving otherwise some tests are failing: https://prow.ci.openshift.org/view/gs/test-platform-results/pr-logs/pull/openshift-knative_serving/832/pull-ci-openshift-knative-serving-release-v1.15-415-test-e2e-aws-415/1831386928168046592

[mgencur]

/hold Hmm. This can probably be achieved by https://github.com/openshift-knative/hack/commit/2f77409a4ee5217c3b9d8450f0f335e9f73d6e42

Update: The same could be achieved by calling bin/generate multple times, each time specifying a different symlink (for the "readiness" image from Serving that would be --sym-link-names "/ko-app/readiness". So this would mean calling bin/generate at least 3 times in Serving (one for all images, second time for "readiness", third time for "runtime" image)).

I think the stuff I implemented can work together with the symlinks. The command can be then called just once in Serving, like this:

$(go env GOPATH)/bin/generate \
  --root-dir "${repo_root_dir}" \
  --generators dockerfile \
  --app-file-fmt "/ko-app/%s" \
  --dockerfile-image-builder-fmt "registry.ci.openshift.org/openshift/release:rhel-8-release-golang-%s-openshift-4.17"

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mgencur, pierDipi

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[pierDipi]

I think since this makes bash scripts easier, let's just do it even though it could be achieved differently

[mgencur]

/unhold