Support for defining custom response type

[DalmasN]

Being able to define custom return types is useful and opens up for cleaner code. Currently the response is types as unknown and often leads the developer to using type assertions.

// Example with type assertions (current way)

type User = {
    id: string;
    name: string;
}

const [user, setUser] = useState<User|null>(null);

requester
    .doGet({
        url: router.getStandaloneUrl("/user"),
    })
    .then((userData) => {
        setUser(userData as User); // userData is unknown
    })

// Example using generics (proposed new way)

type User = {
    id: string;
    name: string;
}

const [user, setUser] = useState<User|null>(null);

requester
    .doGet<User>({
        url: router.getStandaloneUrl("/user"),
    })
    .then((userData) => {
        setUser(userData); // userData is of type User
    })