add subscription process endpoint

src/Resources/SubscriptionProcess.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace D3\KlicktippPhpClient\Resources;
+
+use D3\KlicktippPhpClient\Entities\Subscription as SubscriptionEntity;
+use D3\KlicktippPhpClient\Exceptions\BaseException;
+use GuzzleHttp\Exception\GuzzleException;
+use GuzzleHttp\RequestOptions;
+
+class SubscriptionProcess extends Model
+{
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function index(): array
+    {
+        return $this->connection->requestAndParse(
+            'GET',
+            'list'
+        );
+    }
+
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function get(string $listId): SubscriptionEntity
+    {
+        $data = $this->connection->requestAndParse(
+            'GET',
+            'list/'.urlencode(trim($listId))
+        );
+
+        return new SubscriptionEntity($data);
+    }
+
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function redirect(string $listId, string $email): string
+    {
+        return current(
+            $this->connection->requestAndParse(
+                'POST',
+                'list/redirect',
+                [
+                    RequestOptions::FORM_PARAMS => [
+                        'listid'    => trim($listId),
+                        'email'     => trim($email),
+                    ]
+                ]
+            )
+        );
+    }
+}