chore: bootstrap module from working instance and add install guide

models/DonationSubscription.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace humhub\modules\donations\models;
+
+use humhub\components\ActiveRecord;
+
+class DonationSubscription extends ActiveRecord
+{
+    public static function tableName()
+    {
+        return 'rescue_donation_subscription';
+    }
+
+    public function rules()
+    {
+        return [
+            [['contentcontainer_id', 'provider', 'provider_subscription_id', 'status', 'amount'], 'required'],
+            [['contentcontainer_id', 'donor_user_id', 'goal_id', 'interval_count'], 'integer'],
+            [['amount'], 'number', 'min' => 0.01],
+            [['provider', 'status'], 'string', 'max' => 32],
+            [['provider_subscription_id'], 'string', 'max' => 190],
+            [['currency'], 'string', 'max' => 8],
+            [['interval_unit'], 'string', 'max' => 16],
+        ];
+    }
+
+    public function beforeSave($insert)
+    {
+        if (!parent::beforeSave($insert)) {
+            return false;
+        }
+
+        $now = date('Y-m-d H:i:s');
+        if ($insert && empty($this->created_at)) {
+            $this->created_at = $now;
+        }
+        $this->updated_at = $now;
+
+        if (empty($this->currency)) {
+            $this->currency = 'USD';
+        }
+
+        return true;
+    }
+}