Add utm_campaign to the hosting links

According to where in the app the link was clicked

src/utils/HostingLink.js

@@ -0,0 +1,37 @@
+/*
+Copyright 2019 New Vector Ltd.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import url from 'url';
+import qs from 'qs';
+
+import SdkConfig from '../SdkConfig';
+
+export function getHostingLink(campaign) {
+    const hostingLink = SdkConfig.get().hosting_signup_link;
+    if (!hostingLink) return null;
+    if (!campaign) return hostingLink;
+
+    try {
+        const hostingUrl = url.parse(hostingLink);
+        const params = qs.parse(hostingUrl.query);
+        params.utm_campaign = campaign;
+        hostingUrl.search = undefined;
+        hostingUrl.query = params;
+        return hostingUrl.format();
+    } catch (e) {
+        return hostingLink;
+    }
+}