Configurable API domain

[romalytvynenko]

We have one application where we use a subdomain for the api. It would be good to have an option to configure the domain for the api and maybe an option for the docs path.

'api_domain' => env('API_DOMAIN'),
'api_path' => '',
'docs_path => 'docs'

If the domain is set, the routes could be filtered by default:

Scramble::routes(fn (Route $route) => $route->getDomain() === config('scramble.api_domain'));

Originally posted by @m-lotze in #45