Fix: $apiFetch promise returns void instead of dynamic type

[davide-granello]

Fixed ApiFetch type, now returning Promise< T > instead of Promise< void >. This way main project can declare type returned by the promise dynamically. Example:

const fetchTest = async () => {
        // we now can define response type MyType 
        const response : MyType = await $apiFetch(`backend.test/api/test`, {
            method: 'GET'
        })
        // ...
    }

[kreejzak]

Thanks!