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/Contracts/Serializable.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Laravel\SerializableClosure\Contracts;
+
+interface Serializable
+{
+    /**
+     * Resolve the closure with the given arguments.
+     *
+     * @return mixed
+     */
+    public function __invoke();
+
+    /**
+     * Gets the closure that got serialized/unserialized.
+     *
+     * @return \Closure
+     */
+    public function getClosure();
+}

docker/streamline-src/vendor/laravel/serializable-closure/src/Contracts/Signer.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Laravel\SerializableClosure\Contracts;
+
+interface Signer
+{
+    /**
+     * Sign the given serializable.
+     *
+     * @param  string  $serializable
+     * @return array
+     */
+    public function sign($serializable);
+
+    /**
+     * Verify the given signature.
+     *
+     * @param  array  $signature
+     * @return bool
+     */
+    public function verify($signature);
+}