Built-in flowfile templates

[jahvon]

Enhancement Summary

Common flowfile templates should be added to provide an easy executable init experience.

Templates considering:

• go module (go build, go run with env input, go debug)
• kube (helm install/kubectl apply, kubectl logs, describe/get, etc)
• shell (run with env input)
• ...

Sample usage:

flow template generate -t std:go -w my-ws
flow template generate -t std:kube -w my-ws

Additional context

The built-in templates will need to be under a namespace to avoid conflicts