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/laravel/serializable-closure/src/Serializers/Signed.php

@@ -0,0 +1,91 @@
+<?php
+
+namespace Laravel\SerializableClosure\Serializers;
+
+use Laravel\SerializableClosure\Contracts\Serializable;
+use Laravel\SerializableClosure\Exceptions\InvalidSignatureException;
+use Laravel\SerializableClosure\Exceptions\MissingSecretKeyException;
+
+class Signed implements Serializable
+{
+    /**
+     * The signer that will sign and verify the closure's signature.
+     *
+     * @var \Laravel\SerializableClosure\Contracts\Signer|null
+     */
+    public static $signer;
+
+    /**
+     * The closure to be serialized/unserialized.
+     *
+     * @var \Closure
+     */
+    protected $closure;
+
+    /**
+     * Creates a new serializable closure instance.
+     *
+     * @param  \Closure  $closure
+     * @return void
+     */
+    public function __construct($closure)
+    {
+        $this->closure = $closure;
+    }
+
+    /**
+     * Resolve the closure with the given arguments.
+     *
+     * @return mixed
+     */
+    public function __invoke()
+    {
+        return call_user_func_array($this->closure, func_get_args());
+    }
+
+    /**
+     * Gets the closure.
+     *
+     * @return \Closure
+     */
+    public function getClosure()
+    {
+        return $this->closure;
+    }
+
+    /**
+     * Get the serializable representation of the closure.
+     *
+     * @return array
+     */
+    public function __serialize()
+    {
+        if (! static::$signer) {
+            throw new MissingSecretKeyException();
+        }
+
+        return static::$signer->sign(
+            serialize(new Native($this->closure))
+        );
+    }
+
+    /**
+     * Restore the closure after serialization.
+     *
+     * @param  array  $signature
+     * @return void
+     *
+     * @throws \Laravel\SerializableClosure\Exceptions\InvalidSignatureException
+     */
+    public function __unserialize($signature)
+    {
+        if (static::$signer && ! static::$signer->verify($signature)) {
+            throw new InvalidSignatureException();
+        }
+
+        /** @var \Laravel\SerializableClosure\Contracts\Serializable $serializable */
+        $serializable = unserialize($signature['serializable']);
+
+        $this->closure = $serializable->getClosure();
+    }
+}