Add labels to render

[arminbuerkle]

Fixes #3482.

Description
Adds the --label option to skaffold render.

@nkubala didn't have much time the last weeks, but here is the follow up of #3110 (comment)

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes unit tests
• Mentions any output changes.
• Adds documentation as needed: user docs, YAML reference, CLI reference.
• Adds integration tests if needed.

Reviewer Notes

• The code flow looks good.
• Unit test added.
• User facing changes look good.

Release Notes
Add --label option to skaffold render

[codecov]

Codecov Report

Merging #3558 into master will increase coverage by 0.07%.
The diff coverage is 76.92%.

Impacted Files	Coverage Δ
pkg/skaffold/deploy/deploy.go	100% <ø> (ø)	⬆️
cmd/skaffold/app/cmd/flags.go	100% <ø> (ø)	⬆️
pkg/skaffold/runner/render.go	0% <0%> (ø)	⬆️
pkg/skaffold/deploy/kustomize.go	71.62% <100%> (ø)	⬆️
pkg/skaffold/deploy/deploy_mux.go	89.13% <100%> (ø)	⬆️
pkg/skaffold/deploy/helm.go	78.64% <100%> (ø)	⬆️
pkg/skaffold/deploy/kubectl.go	66.4% <71.42%> (+0.52%)	⬆️
pkg/skaffold/schema/defaults/defaults.go	91.44% <0%> (-2.97%)	⬇️
pkg/skaffold/initializer/init.go	64.81% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/init.go	100% <0%> (ø)	⬆️
... and 6 more

[tejal29]

was there a reason for adding this in input?

  metadata
     namespace: default

[arminbuerkle]

Yes! If metadata doesn't exist, the default labeller doesn't execute, therefore not adding any labels.

Without it skaffold.dev/deployer: kubectl won't be added.

[tejal29]

@arminbuerkle i rebased your branch on latest master and added another test

+               {
+                       description: "single kustomization with user labels",
+                       builds: []build.Artifact{
+                               {
+                                       ImageName: "gcr.io/project/image1",
+                                       Tag:       "gcr.io/project/image1:tag1",
+                               },
+                               {
+                                       ImageName: "gcr.io/project/image2",
+                                       Tag:       "gcr.io/project/image2:tag2",
+                               },
+                       },
+                       labels: []Labeller{
+                               &testLabels{
+                                       labels: map[string]string{
+                                               "user/label": "test",
+                                       }},
+                       },
+                       kustomizations: []kustomizationCall{
+                               {
+                                       folder: ".",
+                                       buildResult: `apiVersion: v1
+kind: Pod
+metadata:
+  namespace: default
+spec:
+  containers:
+  - image: gcr.io/project/image1
+    name: image1
+  - image: gcr.io/project/image2
+    name: image2
+`,
+                               },
+                       },
+                       expected: `apiVersion: v1
+kind: Pod
+metadata:
+  labels:
+    skaffold.dev/deployer: kustomize
+    user/label: test
+  namespace: default

If you give me permission to push to your branch, i can update this PR and merge it.

[arminbuerkle]

If you give me permission to push to your branch, i can update this PR and merge it.

@tejal29 i added you as a collaborator to our repository. For some reason i don't have the allow maintainers to edit checkbox in this PR?

[tejal29]

@arminbuerkle i got the request! Thanks!