Allow custom headers in request

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I need to add custom headers like "X-Include". I have extended code after this line

JSON-API-Client/src/JsonApiClient.php

Line 139 in 5769305

$httpRequest = $this->requestFactory->createRequest($request->method(), $request->uri());

foreach($request->headers()->all() as $header => $value) {
    $httpRequest = $httpRequest->withHeader($header, $value);
}