Feature: #88871 - Handle middleware handler in RequestFactory

See Issue #88871

Description

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 \TYPO3\CMS\Core\Http\RequestFactory builds a handler stack based on the $GLOBALS['TYPO3_CONF_VARS']['HTTP']['handler'] array and injects it into the created client.

Impact

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

Example:

# Add custom middleware to default Guzzle handler stack
$GLOBALS['TYPO3_CONF_VARS']['HTTP']['handler'][] =
   (\TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\ACME\Middleware\Guzzle\CustomMiddleware::class))->handler();
$GLOBALS['TYPO3_CONF_VARS']['HTTP']['handler'][] =
   (\TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\ACME\Middleware\Guzzle\SecondCustomMiddleware::class))->handler();