Generate template files from kctrl package init

**Describe the problem/challenge you have**

I want to generate a template carvel package from command of kctrl package init for quickly to know carvel package.

**Describe the solution you'd like**

Auto generate files (from https://github.com/carvel-dev/ytt/tree/develop/examples/playground/basics/example-demo) :

defaults.yml
```shell
#@data/values
---
echos:
- name: first
- name: second
port: 8081
text: "Hello #ytt World on 8081!"
```

demo.yml
```shell
#@ load("@ytt:data", "data")

#@ def labels():
app: echo
org: test
#@ end

#@ def name(echo):
#@ return "echo-"+echo.name
#@ end

kind: Pod
apiVersion: v1
metadata:
name: echo-app
labels: #@ labels()
spec:
containers:
#@ for/end echo in data.values.echos:
- name: #@ name(echo)
image: hashicorp/http-echo
args:
- #@ "-listen=:" + str(echo.port)
- #@ "-text=" + echo.text

#@ if/end data.values.service.enabled:
---
kind: Service
apiVersion: v1
metadata:
name: echo-service
spec:
selector: #@ labels()
ports:
#@ for/end echo in data.values.echos:
- name: #@ name(echo)
port: #@ echo.port

```

schema.yml
```yaml
#@data/values-schema
---
echos:
- name: ""
port: 8080
text: "Hello #ytt World on 8080!"
service:
enabled: true

```

**Anything else you would like to add:**

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