Add rock for net-istio-webhook

[misohu]

Closes: canonical/knative-operators#237

This Rock is based on upstream ko image: https://console.cloud.google.com/gcr/images/knative-releases/GLOBAL/knative.dev/net-istio/cmd/webhook

To compare the rock I was using the latest upstream docker tag v1.12.3 (that is also the version we are using in knative in kubeflow 1.9 bundle).

Steps for local comparison test

# build the ROCK
rockcraft clean && rockcraft pack --verbosity=trace
sudo rockcraft.skopeo --insecure-policy copy oci-archive:net-istio-webhook_v1.12.3_amd64.rock docker-daemon:net-istio-webhook:v1.12.3

# Upstream image 
docker run gcr.io/knative-releases/knative.dev/net-istio/cmd/webhook:v1.12.3

## Output
2024/11/12 08:27:01 Error building kubeconfig: failed to create client config: invalid configuration: no configuration has been provided, try setting KUBERNETES_MASTER environment variable

########################################################

# Rock 
docker run net-istio-webhook:v1.12.3

# Output
2024-11-12T08:27:57.781Z [pebble] Started daemon.
2024-11-12T08:27:57.815Z [pebble] POST /v1/services 16.172341ms 202
2024-11-12T08:27:57.832Z [pebble] Service "net-istio-webhook" starting: /ko-app/webhook
2024-11-12T08:27:57.975Z [pebble] Change 1 task (Start service "net-istio-webhook") failed: cannot start service: exited quickly with code 1
2024-11-12T08:27:58.016Z [pebble] GET /v1/changes/1/wait 199.692146ms 200
2024-11-12T08:27:58.017Z [pebble] Started default services with change 1.

# Output for service is hidden you need to get the id of running docker container 
docker ps
# bash into the container 
docker exec -ti <your_id> bash
# execute the service command manually
# Output
2024/11/12 08:29:29 Error building kubeconfig: failed to create client config: invalid configuration: no configuration has been provided, try setting KUBERNETES_MASTER environment variable

[mvlassis]

All sanity tests pass, and the output is as expected :)

[mvlassis]

All good, but note that we have this issue which blocks us from integration.