Implement Keystone environment deployments

app/Enums/EnvironmentVariableSource.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace App\Enums;
+
+use App\Enums\Concerns\Arrayable;
+
+enum EnvironmentVariableSource: string
+{
+    use Arrayable;
+
+    case USER = 'user';
+    case MANAGED_ATTACHMENT = 'managed_attachment';
+    case SYSTEM = 'system';
+}