[Explore] Save custom url parameters when user save slices (#4578)

* [Explore] Save url parameters when user save slices

* remove print

(cherry picked from commit bd9ecbe)

* add unit test

(cherry picked from commit 0f350ad)

* wrapping all request params into url_params

(cherry picked from commit 17197c1)

superset/assets/javascripts/explore/stores/store.js

@@ -109,6 +109,13 @@ export function applyDefaultFormData(form_data) {
       formData[k] = form_data[k];
     }
   });
+  // fill in additional params stored in form_data but not used by control
+  Object.keys(form_data)
+    .forEach((key) => {
+      if (formData[key] === undefined) {
+        formData[key] = form_data[key];
+      }
+    });
   return formData;
 }