Fix wkhtmltopdf bugs

The wkhtmltopdf library does not work with the latest version of alpine. To
workaround this, a known working image based on an older alpine image is pulled
in and relevant libraries copied to the target image.

The `snappy` package required a few updates to support this, including setting
the wkhtmltopdf binary path explicitly and to enable access to local files
(disabled by default).

docker/snappy.php

@@ -0,0 +1,56 @@
+<?php
+
+$pdfPath = '/usr/bin/wkhtmltopdf';
+$imagePath = '/usr/bin/wkhtmltoimage';
+
+return [
+    /*
+      |--------------------------------------------------------------------------
+      | Snappy PDF / Image Configuration
+      |--------------------------------------------------------------------------
+      |
+      | This option contains settings for PDF generation.
+      |
+      | Enabled:
+      |
+      |    Whether to load PDF / Image generation.
+      |
+      | Binary:
+      |
+      |    The file path of the wkhtmltopdf / wkhtmltoimage executable.
+      |
+      | Timout:
+      |
+      |    The amount of time to wait (in seconds) before PDF / Image generation is stopped.
+      |    Setting this to false disables the timeout (unlimited processing time).
+      |
+      | Options:
+      |
+      |    The wkhtmltopdf command options. These are passed directly to wkhtmltopdf.
+      |    See https://wkhtmltopdf.org/usage/wkhtmltopdf.txt for all options.
+      |
+      | Env:
+      |
+      |    The environment variables to set while running the wkhtmltopdf process.
+      |
+     */
+
+    'pdf' => [
+        'enabled' => true,
+        'binary' => $pdfPath,
+        'timeout' => false,
+        'options' => [
+            'enable-local-file-access' => true
+        ],
+        'env' => [],
+    ],
+    'image' => [
+        'enabled' => true,
+        'binary' => $imagePath,
+        'timeout' => false,
+        'options' => [
+            'enable-local-file-access' => true
+        ],
+        'env' => [],
+    ],
+];