Deferrable config option proof of concept

[emmadesilva]

'header' => defer(fn () => config('hyde.name').' Docs'),
'header' => defer(fn ($config) => "{$config['hyde.name']} Docs"),
'header' => defer(fn (\Illuminate\Config\Repository $config): string => "{$config->get('hyde.name')} Docs"),

[emmadesilva]

Closing for now as I don't think it's intuitive enough to warrant the complexity