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/Test/Constraint/EmailHeaderSame.php

@@ -0,0 +1,62 @@
+<?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\Test\Constraint;
+
+use PHPUnit\Framework\Constraint\Constraint;
+use Symfony\Component\Mime\Header\UnstructuredHeader;
+use Symfony\Component\Mime\RawMessage;
+
+final class EmailHeaderSame extends Constraint
+{
+    private string $headerName;
+    private string $expectedValue;
+
+    public function __construct(string $headerName, string $expectedValue)
+    {
+        $this->headerName = $headerName;
+        $this->expectedValue = $expectedValue;
+    }
+
+    public function toString(): string
+    {
+        return sprintf('has header "%s" with value "%s"', $this->headerName, $this->expectedValue);
+    }
+
+    /**
+     * @param RawMessage $message
+     */
+    protected function matches($message): bool
+    {
+        if (RawMessage::class === $message::class) {
+            throw new \LogicException('Unable to test a message header on a RawMessage instance.');
+        }
+
+        return $this->expectedValue === $this->getHeaderValue($message);
+    }
+
+    /**
+     * @param RawMessage $message
+     */
+    protected function failureDescription($message): string
+    {
+        return sprintf('the Email %s (value is %s)', $this->toString(), $this->getHeaderValue($message) ?? 'null');
+    }
+
+    private function getHeaderValue($message): ?string
+    {
+        if (null === $header = $message->getHeaders()->get($this->headerName)) {
+            return null;
+        }
+
+        return $header instanceof UnstructuredHeader ? $header->getValue() : $header->getBodyAsString();
+    }
+}