Allow StreamInterface as raw HTTP Client body (#49705)

* Allow StreamInterface as raw HTTP Client body

Since the body payload is passed through to Guzzle, which in turn can
handle Streams as well, this extends the versatility of the HTTP Client

* Update PendingRequest.php

---------

Co-authored-by: Taylor Otwell <taylor@laravel.com>

Client/PendingRequest.php

@@ -78,7 +78,7 @@ class PendingRequest
     /**
      * The raw body for the request.
      *
-     * @var string
+     * @var \Psr\Http\Message\StreamInterface|string
      */
     protected $pendingBody;
 
@@ -259,7 +259,7 @@ public function baseUrl(string $url)
     /**
      * Attach a raw body to the request.
      *
-     * @param  string  $content
+     * @param  \Psr\Http\Message\StreamInterface|string  $content
      * @param  string  $contentType
      * @return $this
      */