🐛 (go/v4): Simplify init directory validation to only block PROJECT file

[camilamacedo86]

Remove overly restrictive directory validation that was blocking legitimate
files like mise.toml and other configuration files. The previous logic
attempted to allow only specific file types but had inverted logic that
blocked most files unnecessarily.

At this stage, we don't have a maintainable way to accurately predict all
possible file conflicts. The only file that definitively conflicts with
scaffolding is the PROJECT file, which kubebuilder generates.

This allows users to run kubebuilder init in directories with legitimate
configuration files (mise.toml, .envrc, .tool-versions, etc.) without
encountering false validation errors.

Closes: #5143

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[robinlioret]

It looks a lot more permissive that what is in place at the moment. Will kubebuilder override existing files ?
I'm thinking about custom GitHub workflow files or git ignore or any common files.

I don't thinks it'll an issue for experienced people since we just have to look a the git diff and reset the files we want to keep as is. But it may be a good idea to add this hack to the documentation, what do you think ?

[camilamacedo86]

/hold

We need think more about.
Maybe warning and make clear that the project has not a empty dir and files can be overwrite OR conflicts be faced

[robinlioret]

I have no idea what amount of work it could represent hut why not adding a step before generating the files ?

Something like:

1. Queue files to generate in a list
2. Check if one of them is going to be overwritten
3. Display a warning with a interactive choice for the user

This way, we get rid of the need for hack documentation while keeping flexibility and automated maintenance of the kubebuilder "reserved" files.