FIX: ensures period-chooser is not losing query params (#10534)

eg repro before:
- visit http://pr-discourse.test/top/weekly?f=foo
- select another period in the period chooser
- f=foo was gone

After this commit it should still be present

app/assets/javascripts/discourse/app/controllers/discovery.js

@@ -3,11 +3,13 @@ import Controller, { inject as controller } from "@ember/controller";
 import DiscourseURL from "discourse/lib/url";
 import Category from "discourse/models/category";
 import { observes } from "discourse-common/utils/decorators";
+import { inject as service } from "@ember/service";
 
 export default Controller.extend({
   discoveryTopics: controller("discovery/topics"),
   navigationCategory: controller("navigation/category"),
   application: controller(),
+  router: service(),
 
   loading: false,
 
@@ -32,6 +34,16 @@ export default Controller.extend({
     }
 
     url += "/top/" + period;
+
+    const queryParams = this.router.currentRoute.queryParams;
+    if (Object.keys(queryParams).length) {
+      url =
+        `${url}?` +
+        Object.keys(queryParams)
+          .map(key => `${key}=${queryParams[key]}`)
+          .join("&");
+    }
+
     return url;
   },