Introduce `pkl project init` to create a project aka `PklProject`

Go has something similar with `go mod init`.

Creating a `PklProject` by hand is possible, but I think it would be a nice convenient function to inrtoduce `pkl project init`.
It will create a `PklProject` and `PklProject.deps.json` with some base setup?!

```pkl
amends "pkl:Project"

package {
name = "some.name" // Maybe we can support here pkl project init --name "my.awesome.project"
baseUri = "package://pkg.pkl-lang.org/github.com/[owner/name]/\(name)"
version = "0.1.0"
packageZipUrl = "https://github.com/[repo/name]/releases/download/\(name)@\(version)/\(name)@\(version).zip"
description = "TODO"
authors {
"PlaceHolder "
}
website = "https://github.com/[owner/name]"
sourceCode = "https://github.com/[owner/name]"
license = "TODO"
issueTracker = "https://github.com/[owner/name]/issues"
}

dependencies {
// Add dependencies here
}
```

```pkl
{
"schemaVersion": 1,
"resolvedDependencies": {}
}
```

The placeholders and waht we put in should be discussed of course.
But maybe this gives especially new comes a better onboarding to pkl.
No need to find out that it is possible to create a PklProject and how to set it up etc.

We should also discuss if what cli options we support.
`name` is a good candidate I guess.
`website` etc. might be a bit too mucy?! 🤔 🤷

Start by reviewing the existing `pkl project` CLI entry point and how `PklProject` and `PklProject.deps.json` are currently created or loaded. Clarify the supported options and placeholder values with maintainers; done means `pkl project init` creates the agreed project files with the expected base setup.

Written by the indexing model from the issue text.