Modify panel default() method to accept closure

[binaryfire]

I've got 2 separate domains with their own guards, panels and auth pages. I'm running into issues when Filament uses default() under the hood because each domain needs a different default panel. Closures make the default() method more flexible and allow for things like this:

// Admin domain default panel
->default(fn (): bool => CurrentDomain::isAdminDomain())

// Member domain default panel
->default(fn (): bool => CurrentDomain::isMemberDomain())