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/event-dispatcher-contracts/Event.php

@@ -0,0 +1,51 @@
+<?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\Contracts\EventDispatcher;
+
+use Psr\EventDispatcher\StoppableEventInterface;
+
+/**
+ * Event is the base class for classes containing event data.
+ *
+ * This class contains no event data. It is used by events that do not pass
+ * state information to an event handler when an event is raised.
+ *
+ * You can call the method stopPropagation() to abort the execution of
+ * further listeners in your event listener.
+ *
+ * @author Guilherme Blanco <guilhermeblanco@hotmail.com>
+ * @author Jonathan Wage <jonwage@gmail.com>
+ * @author Roman Borschel <roman@code-factory.org>
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ * @author Nicolas Grekas <p@tchwork.com>
+ */
+class Event implements StoppableEventInterface
+{
+    private bool $propagationStopped = false;
+
+    public function isPropagationStopped(): bool
+    {
+        return $this->propagationStopped;
+    }
+
+    /**
+     * Stops the propagation of the event to further event listeners.
+     *
+     * If multiple event listeners are connected to the same event, no
+     * further event listener will be triggered once any trigger calls
+     * stopPropagation().
+     */
+    public function stopPropagation(): void
+    {
+        $this->propagationStopped = true;
+    }
+}