This new command allows users to extract templates for authoring
(customization) without the complexity of finding and downloading a
specific directory for their versioned artifact.

Example usage:

```
openapi-generator author template -g java --library webclient
```

This will write all templates with library-specific templates to the
'./out' directory relative to the current directory.

CLI will refer the user to
https://openapi-generator.tech/docs/templating after generation