Allow customization of what is sent to `fetch` function

[stazz]

The following properties should be added to HTTPEndpointCallerOptions:

• resourceInit?: (args: FetchCustomizationParameters) => URL | Request
• requestInit?: RequestInitCustomization | ((args: FetchCustomizationParametrs<URL | Request>) => RequestInitCustomization)

export interface FetchCustomizationParameters<TResource = URL> {
  resource: TResource;
  method: data.HttpMethod;
  body: string | undefined;
  headers: Record<string, data.HeaderValue> | undefined;
}

export type RequestInitCustomization = Omit<RequestInit, "method" | "body" | "headers">;

[stazz]

Notice that this also makes this package unusuable for consumer which don't have DOM as lib, or augmented global namespace with fetch-related things. Therefore, this issue should be done for next major release.