Site selector.
type SitesField<T extends Record<string, any>> = SiteReference<T> | SiteReference<T>[];
type AllSites = SitesField<{ is_active: boolean }>;
// Result: {
// handle: string;
// name: string;
// lang: string;
// locale: string;
// short_locale: string;
// url: string;
// permalink: string;
// direction: "ltr" | "rtl";
// attributes: { is_active: boolean };
// } | {
// handle: string;
// name: string;
// lang: string;
// locale: string;
// short_locale: string;
// url: string;
// permalink: string;
// direction: "ltr" | "rtl";
// attributes: { is_active: boolean };
// }[]