Implement Keystone environment deployments

app/Models/EnvironmentVariable.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Models;
+
+use App\Enums\EnvironmentVariableSource;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class EnvironmentVariable extends Model
+{
+    protected $guarded = [];
+
+    protected function casts(): array
+    {
+        return [
+            'value' => 'encrypted',
+            'source' => EnvironmentVariableSource::class,
+            'overridable' => 'boolean',
+        ];
+    }
+
+    public function environment(): BelongsTo
+    {
+        return $this->belongsTo(Environment::class);
+    }
+
+    public function serviceSlice(): BelongsTo
+    {
+        return $this->belongsTo(ServiceSlice::class);
+    }
+}