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/Crypto/SMimeEncrypter.php

@@ -0,0 +1,63 @@
+<?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\Crypto;
+
+use Symfony\Component\Mime\Exception\RuntimeException;
+use Symfony\Component\Mime\Message;
+
+/**
+ * @author Sebastiaan Stok <s.stok@rollerscapes.net>
+ */
+final class SMimeEncrypter extends SMime
+{
+    private string|array $certs;
+    private int $cipher;
+
+    /**
+     * @param string|string[] $certificate The path (or array of paths) of the file(s) containing the X.509 certificate(s)
+     * @param int|null        $cipher      A set of algorithms used to encrypt the message. Must be one of these PHP constants: https://www.php.net/manual/en/openssl.ciphers.php
+     */
+    public function __construct(string|array $certificate, ?int $cipher = null)
+    {
+        if (!\extension_loaded('openssl')) {
+            throw new \LogicException('PHP extension "openssl" is required to use SMime.');
+        }
+
+        if (\is_array($certificate)) {
+            $this->certs = array_map($this->normalizeFilePath(...), $certificate);
+        } else {
+            $this->certs = $this->normalizeFilePath($certificate);
+        }
+
+        $this->cipher = $cipher ?? \OPENSSL_CIPHER_AES_256_CBC;
+    }
+
+    public function encrypt(Message $message): Message
+    {
+        $bufferFile = tmpfile();
+        $outputFile = tmpfile();
+
+        $this->iteratorToFile($message->toIterable(), $bufferFile);
+
+        if (!@openssl_pkcs7_encrypt(stream_get_meta_data($bufferFile)['uri'], stream_get_meta_data($outputFile)['uri'], $this->certs, [], 0, $this->cipher)) {
+            throw new RuntimeException(sprintf('Failed to encrypt S/Mime message. Error: "%s".', openssl_error_string()));
+        }
+
+        $mimePart = $this->convertMessageToSMimePart($outputFile, 'application', 'pkcs7-mime');
+        $mimePart->getHeaders()
+            ->addTextHeader('Content-Transfer-Encoding', 'base64')
+            ->addParameterizedHeader('Content-Disposition', 'attachment', ['name' => 'smime.p7m'])
+        ;
+
+        return new Message($message->getHeaders(), $mimePart);
+    }
+}