fix(branding): Use config url for dynamic branding

config.js

          logoImageUrl: 'https://example.com/logo-img.png'
      }
     */
-    // brandingDataUrl: '',
+    // dynamicBrandingUrl: '',
 
     // The URL of the moderated rooms microservice, if available. If it
     // is present, a link to the service will be rendered on the welcome page,

react/features/dynamic-branding/actions.js

     SET_DYNAMIC_BRANDING_FAILED,
     SET_DYNAMIC_BRANDING_READY
 } from './actionTypes';
-import { extractFqnFromPath } from './functions';
+import { getDynamicBrandingUrl } from './functions';
 
 const logger = getLogger(__filename);
 
+
 /**
  * Fetches custom branding data.
  * If there is no data or the request fails, sets the `customizationReady` flag
 export function fetchCustomBrandingData() {
     return async function(dispatch: Function, getState: Function) {
         const state = getState();
-        const baseUrl = state['features/base/config'].brandingDataUrl;
         const { customizationReady } = state['features/dynamic-branding'];
 
         if (!customizationReady) {
-            const fqn = extractFqnFromPath(state['features/base/connection'].locationURL.pathname);
+            const url = getDynamicBrandingUrl(state);
 
-            if (baseUrl && fqn) {
+            if (url) {
                 try {
-                    const res = await doGetJSON(`${baseUrl}?conferenceFqn=${encodeURIComponent(fqn)}`);
+                    const res = await doGetJSON(url);
 
                     return dispatch(setDynamicBrandingData(res));
                 } catch (err) {

react/features/dynamic-branding/functions.js

 
     return parts.length > 2 ? `${parts[len - 2]}/${parts[len - 1]}` : '';
 }
+
+/**
+ * Returns the url used for fetching dynamic branding.
+ *
+ * @param {Object} state - The state of the app.
+ * @returns {string}
+ */
+export function getDynamicBrandingUrl(state: Object) {
+    const { dynamicBrandingUrl } = state['features/base/config'];
+
+    if (dynamicBrandingUrl) {
+        return dynamicBrandingUrl;
+    }
+
+    const baseUrl = state['features/base/config'].brandingDataUrl;
+    const fqn = extractFqnFromPath(state['features/base/connection'].locationURL.pathname);
+
+    if (baseUrl && fqn) {
+        return `${baseUrl}?conferenceFqn=${encodeURIComponent(fqn)}`;
+    }
+}