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/mime/RawMessage.php

@@ -0,0 +1,91 @@
+<?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\Mime;
+
+use Symfony\Component\Mime\Exception\LogicException;
+
+/**
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+class RawMessage
+{
+    private iterable|string $message;
+    private bool $isGeneratorClosed;
+
+    public function __construct(iterable|string $message)
+    {
+        $this->message = $message;
+    }
+
+    public function toString(): string
+    {
+        if (\is_string($this->message)) {
+            return $this->message;
+        }
+
+        $message = '';
+        foreach ($this->message as $chunk) {
+            $message .= $chunk;
+        }
+
+        return $this->message = $message;
+    }
+
+    public function toIterable(): iterable
+    {
+        if ($this->isGeneratorClosed ?? false) {
+            trigger_deprecation('symfony/mime', '6.4', 'Sending an email with a closed generator is deprecated and will throw in 7.0.');
+            // throw new LogicException('Unable to send the email as its generator is already closed.');
+        }
+
+        if (\is_string($this->message)) {
+            yield $this->message;
+
+            return;
+        }
+
+        if ($this->message instanceof \Generator) {
+            $message = '';
+            foreach ($this->message as $chunk) {
+                $message .= $chunk;
+                yield $chunk;
+            }
+            $this->isGeneratorClosed = !$this->message->valid();
+            $this->message = $message;
+
+            return;
+        }
+
+        foreach ($this->message as $chunk) {
+            yield $chunk;
+        }
+    }
+
+    /**
+     * @return void
+     *
+     * @throws LogicException if the message is not valid
+     */
+    public function ensureValidity()
+    {
+    }
+
+    public function __serialize(): array
+    {
+        return [$this->toString()];
+    }
+
+    public function __unserialize(array $data): void
+    {
+        [$this->message] = $data;
+    }
+}