🐛 Fix the webhook creation for defaulting webhooks

[prafull01]

Description:
Remove the import k8s.io/apimachinery/pkg/runtime in webhook scaffolding for the defaulting webhooks.

Motivation:
Webhook defaulting scaffolding imports the k8s.io/apimachinery/pkg/runtime which it doesn't use in the code and hence the building of project throws an error.

prafull@EMPID18004:~/go/src/github.com/prafull01/kubebuilder/proj$ ../bin/kubebuilder create webhook --group praf --version v1beta1 --kind Laker --defaulting
Writing scaffold for you to edit...
api/v1beta1/laker_webhook.go
prafull@EMPID18004:~/go/src/github.com/prafull01/kubebuilder/proj$ make 
/home/prafull/go/bin/controller-gen object:headerFile="hack/boilerplate.go.txt" paths="./..."
go fmt ./...
go vet ./...
# sigs.k8s.io/kubebuilder/api/v1beta1
api/v1beta1/laker_webhook.go:20:2: imported and not used: "k8s.io/apimachinery/pkg/runtime"
make: *** [Makefile:51: vet] Error 2```

[k8s-ci-robot]

Hi @prafull01. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[prafull01]

@camilamacedo86 Should we add the tests of --defaulting and --programmatic-validation separately in the generate_testdata.sh. WDYT?

[camilamacedo86]

/ok-to-test

[prafull01]

/retest

[prafull01]

/test pull-kubebuilder-e2e-k8s-1-15-3

[prafull01]

/test pull-kubebuilder-e2e-k8s-1-15-3

[camilamacedo86]

Hi @prafull01,

could you please just fix the nit in the generate_testdata.sh?
Otherwise, it shows great.

/approve

[prafull01]

/test pull-kubebuilder-e2e-k8s-1-16-2

[prafull01]

/retest

[camilamacedo86]

The bug was reproduced locally with the following steps:

kubebuilder init
kubebuilder create api --group ship --version v1beta1 --kind Frigate
kubebuilder create webhook --group ship --version v1beta1 --kind Frigate --defaulting

See the import not used in api/v1beta1/frigate_webhook.go:

And then, by using this PR we can check that it is solved:

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: camilamacedo86, prafull01

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