`kamal init` should offer the option to overwrite files and/or create new ones

Kamal 1.4.0 launched with a new hook (`docker-setup`). I thought that running `kamal init` would offer me the option to revise each file from the setup and overwrite or just create as Rails and many other projects do:

```
Overwrite /Users/luiz/Projects/app/file? (enter "h" for help) [Ynaqdhm]
```

It doesn't, and if you want to get these new files, you either create them manually or just rename `hooks` to, for example, `hooks.old` and then compare the changes in the files.

It would be nice if `init` also offered a diff on the files and created new hooks if they don't exist.

Start by tracing the `kamal init` entry point and how the `docker-setup` hook files are selected. Review the existing setup flow and determine how overwrite prompts, diffs, and missing hook creation should fit; done means `init` can present these choices for existing and new files.

Written by the indexing model from the issue text.