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/mailer/Mailer.php

@@ -0,0 +1,76 @@
+<?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\Mailer;
+
+use Psr\EventDispatcher\EventDispatcherInterface;
+use Symfony\Component\Mailer\Event\MessageEvent;
+use Symfony\Component\Mailer\Exception\TransportExceptionInterface;
+use Symfony\Component\Mailer\Messenger\SendEmailMessage;
+use Symfony\Component\Mailer\Transport\TransportInterface;
+use Symfony\Component\Messenger\Exception\HandlerFailedException;
+use Symfony\Component\Messenger\MessageBusInterface;
+use Symfony\Component\Mime\RawMessage;
+
+/**
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+final class Mailer implements MailerInterface
+{
+    private TransportInterface $transport;
+    private ?MessageBusInterface $bus;
+    private ?EventDispatcherInterface $dispatcher;
+
+    public function __construct(TransportInterface $transport, ?MessageBusInterface $bus = null, ?EventDispatcherInterface $dispatcher = null)
+    {
+        $this->transport = $transport;
+        $this->bus = $bus;
+        $this->dispatcher = $dispatcher;
+    }
+
+    public function send(RawMessage $message, ?Envelope $envelope = null): void
+    {
+        if (null === $this->bus) {
+            $this->transport->send($message, $envelope);
+
+            return;
+        }
+
+        $stamps = [];
+        if (null !== $this->dispatcher) {
+            // The dispatched event here has `queued` set to `true`; the goal is NOT to render the message, but to let
+            // listeners do something before a message is sent to the queue.
+            // We are using a cloned message as we still want to dispatch the **original** message, not the one modified by listeners.
+            // That's because the listeners will run again when the email is sent via Messenger by the transport (see `AbstractTransport`).
+            // Listeners should act depending on the `$queued` argument of the `MessageEvent` instance.
+            $clonedMessage = clone $message;
+            $clonedEnvelope = null !== $envelope ? clone $envelope : Envelope::create($clonedMessage);
+            $event = new MessageEvent($clonedMessage, $clonedEnvelope, (string) $this->transport, true);
+            $this->dispatcher->dispatch($event);
+            $stamps = $event->getStamps();
+
+            if ($event->isRejected()) {
+                return;
+            }
+        }
+
+        try {
+            $this->bus->dispatch(new SendEmailMessage($message, $envelope), $stamps);
+        } catch (HandlerFailedException $e) {
+            foreach ($e->getWrappedExceptions() as $nested) {
+                if ($nested instanceof TransportExceptionInterface) {
+                    throw $nested;
+                }
+            }
+            throw $e;
+        }
+    }
+}