Build modified streamline images

The official image from streamline does not currently work for the arm64
platform. As a temporary measure, the source code and docker build scripts
have been lifted from the official images and are used to build locally.

Some additional modifications are made to reduce overall image size, these
are documented in docker/README.md

docker/streamline-src/vendor/symfony/http-kernel/Event/KernelEvent.php

@@ -0,0 +1,74 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\HttpKernel\Event;
+
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpKernel\HttpKernelInterface;
+use Symfony\Contracts\EventDispatcher\Event;
+
+/**
+ * Base class for events thrown in the HttpKernel component.
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
+class KernelEvent extends Event
+{
+    private HttpKernelInterface $kernel;
+    private Request $request;
+    private ?int $requestType;
+
+    /**
+     * @param int $requestType The request type the kernel is currently processing; one of
+     *                         HttpKernelInterface::MAIN_REQUEST or HttpKernelInterface::SUB_REQUEST
+     */
+    public function __construct(HttpKernelInterface $kernel, Request $request, ?int $requestType)
+    {
+        $this->kernel = $kernel;
+        $this->request = $request;
+        $this->requestType = $requestType;
+    }
+
+    /**
+     * Returns the kernel in which this event was thrown.
+     */
+    public function getKernel(): HttpKernelInterface
+    {
+        return $this->kernel;
+    }
+
+    /**
+     * Returns the request the kernel is currently processing.
+     */
+    public function getRequest(): Request
+    {
+        return $this->request;
+    }
+
+    /**
+     * Returns the request type the kernel is currently processing.
+     *
+     * @return int One of HttpKernelInterface::MAIN_REQUEST and
+     *             HttpKernelInterface::SUB_REQUEST
+     */
+    public function getRequestType(): int
+    {
+        return $this->requestType;
+    }
+
+    /**
+     * Checks if this is the main request.
+     */
+    public function isMainRequest(): bool
+    {
+        return HttpKernelInterface::MAIN_REQUEST === $this->requestType;
+    }
+}