[MM-51236] - Add opt-in checkbox in self-hosted account creation page (#22709)

* [MM-51236] - Add opt-in checkbox in self-hosted account creation page

* add server impl

* fix lint and translations

* add tests

* improvents

* fix model

* fix mocks

* feedback impl

* update text color

* handle error

* fix tests

webapp/platform/client/src/client4.ts

@@ -26,6 +26,7 @@ import {
     CreateSubscriptionRequest,
     Feedback,
     WorkspaceDeletionRequest,
+    NewsletterRequestBody,
 } from '@mattermost/types/cloud';
 import {
     SelfHostedSignupForm,
@@ -3893,6 +3894,13 @@ export default class Client4 {
         );
     };
 
+    subscribeToNewsletter = (newletterRequestBody: NewsletterRequestBody) => {
+        return this.doFetch<StatusOK>(
+            `${this.getHostedCustomerRoute()}/subscribe-newsletter`,
+            {method: 'post', body: JSON.stringify(newletterRequestBody)},
+        );
+    };
+
     createPaymentMethod = async () => {
         return this.doFetch(
             `${this.getCloudRoute()}/payment`,