Refactor bool return type (breaking change, major release)

[ndeet]

We have several places where we only return true in case of success but no false because it throws an exception in that case. As discussed with Wouter we should refactor that to void return type as you have that function in a try/catch block anyway.

e.g. https://github.com/btcpayserver/btcpayserver-greenfield-php/blob/master/src/Client/User.php#L79

if ($response->getStatus() === 200) {
            return true;
        } else {
            throw $this->getExceptionByStatusCode($method, $url, $response);
        }