fix: Runtime config support for feature flags

This makes sure the following feature flags work with dynamic runtime
configuration:

* ENABLE_NEW_EDITOR_PAGES
* ENABLE_UNIT_PAGE
* ENABLE_VIDEO_UPLOAD_PAGE_LINK_IN_CONTENT_DROPDOWN
* ENABLE_TAGGING_TAXONOMY_PAGES

We also remove flags from the `.env*` files that are no longer in use.

src/header/utils.js

@@ -1,3 +1,4 @@
+import { getConfig } from '@edx/frontend-platform';
 import { getPagePath } from '../utils';
 import messages from './messages';
 
@@ -20,7 +21,7 @@ export const getContentMenuItems = ({ studioBaseUrl, courseId, intl }) => {
       title: intl.formatMessage(messages['header.links.filesAndUploads']),
     },
   ];
-  if (process.env.ENABLE_VIDEO_UPLOAD_PAGE_LINK_IN_CONTENT_DROPDOWN === 'true') {
+  if (getConfig().ENABLE_VIDEO_UPLOAD_PAGE_LINK_IN_CONTENT_DROPDOWN === 'true') {
     items.push({
       href: `${studioBaseUrl}/videos/${courseId}`,
       title: intl.formatMessage(messages['header.links.videoUploads']),

src/header/utils.test.js

@@ -1,3 +1,4 @@
+import { getConfig, setConfig } from '@edx/frontend-platform';
 import { getContentMenuItems } from './utils';
 
 const props = {
@@ -11,11 +12,18 @@ const props = {
 describe('header utils', () => {
   describe('getContentMenuItems', () => {
     it('should include Video Uploads option', () => {
+      setConfig({
+        ...getConfig(),
+        ENABLE_VIDEO_UPLOAD_PAGE_LINK_IN_CONTENT_DROPDOWN: 'true',
+      });
       const actualItems = getContentMenuItems(props);
       expect(actualItems).toHaveLength(5);
     });
     it('should not include Video Uploads option', () => {
-      process.env.ENABLE_VIDEO_UPLOAD_PAGE_LINK_IN_CONTENT_DROPDOWN = 'false';
+      setConfig({
+        ...getConfig(),
+        ENABLE_VIDEO_UPLOAD_PAGE_LINK_IN_CONTENT_DROPDOWN: 'false',
+      });
       const actualItems = getContentMenuItems(props);
       expect(actualItems).toHaveLength(4);
     });