Feature: #88871 - Handle middleware handler in RequestFactory correctly

See Issue #88871


Guzzle offers the possibility to register custom middleware handlers during the client initialization. With this feature it is now possible to define those custom handlers in $GLOBALS['TYPO3_CONF_VARS']['HTTP']['handler'] as an array. The RequestFactory builds a handler stack based on the $GLOBALS['TYPO3_CONF_VARS']['HTTP']['handler'] array and injects it into the created client.


The default handler stack (guzzle defaults) will be extended and not overwritten.


# Add custom middleware to default Guzzle handler stack
$GLOBALS['TYPO3_CONF_VARS']['HTTP']['handler'][] =
$GLOBALS['TYPO3_CONF_VARS']['HTTP']['handler'][] =