Make Package class conditionable

[geisi]

Hello Spatie Team!

This is my first PR for this package.
This PR adds the Illuminate\Support\Traits\Conditionable trait to the Package class.

This enhancement empowers package maintainers with the flexibility to tailor their package behavior dynamically. For instance, it enables conditional package configuration as demonstrated below:

public function configurePackage(Package $package): void
{
    ...
    $package->when(config('package.enable_routes', false), fn(Package $package) => $package->hasRoute('package'));
}

I have not added any tests for this since it relies on a Laravel Core functionality, which is well-tested.

Thank you!

[freekmurze]

Thanks for this PR. I'm going to pass on it because I think the vast majority of users of this package do not need.

Those who do can extend our provider and add the trait.