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/config/broadcasting.php

@@ -0,0 +1,58 @@
+<?php
+
+return [
+
+    /*
+    |--------------------------------------------------------------------------
+    | Default Broadcaster
+    |--------------------------------------------------------------------------
+    |
+    | This option controls the default broadcaster that will be used by the
+    | framework when an event needs to be broadcast. You may set this to
+    | any of the connections defined in the "connections" array below.
+    |
+    | Supported: "pusher", "redis", "log", "null"
+    |
+    */
+
+    'default' => env('BROADCAST_DRIVER', 'null'),
+
+    /*
+    |--------------------------------------------------------------------------
+    | Broadcast Connections
+    |--------------------------------------------------------------------------
+    |
+    | Here you may define all of the broadcast connections that will be used
+    | to broadcast events to other systems or over websockets. Samples of
+    | each available type of connection are provided inside this array.
+    |
+    */
+
+    'connections' => [
+
+        'pusher' => [
+            'driver' => 'pusher',
+            'key' => env('PUSHER_APP_KEY'),
+            'secret' => env('PUSHER_APP_SECRET'),
+            'app_id' => env('PUSHER_APP_ID'),
+            'options' => [
+                //
+            ],
+        ],
+
+        'redis' => [
+            'driver' => 'redis',
+            'connection' => 'default',
+        ],
+
+        'log' => [
+            'driver' => 'log',
+        ],
+
+        'null' => [
+            'driver' => 'null',
+        ],
+
+    ],
+
+];