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/guzzlehttp/psr7/src/DroppingStream.php

@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GuzzleHttp\Psr7;
+
+use Psr\Http\Message\StreamInterface;
+
+/**
+ * Stream decorator that begins dropping data once the size of the underlying
+ * stream becomes too full.
+ */
+final class DroppingStream implements StreamInterface
+{
+    use StreamDecoratorTrait;
+
+    /** @var int */
+    private $maxLength;
+
+    /** @var StreamInterface */
+    private $stream;
+
+    /**
+     * @param StreamInterface $stream    Underlying stream to decorate.
+     * @param int             $maxLength Maximum size before dropping data.
+     */
+    public function __construct(StreamInterface $stream, int $maxLength)
+    {
+        $this->stream = $stream;
+        $this->maxLength = $maxLength;
+    }
+
+    public function write($string): int
+    {
+        $diff = $this->maxLength - $this->stream->getSize();
+
+        // Begin returning 0 when the underlying stream is too large.
+        if ($diff <= 0) {
+            return 0;
+        }
+
+        // Write the stream or a subset of the stream if needed.
+        if (strlen($string) < $diff) {
+            return $this->stream->write($string);
+        }
+
+        return $this->stream->write(substr($string, 0, $diff));
+    }
+}