feat: Support runtime configuration (second attempt)

(This reintroduces the change in 9f84230c that was later reverted by
67b0b33a.)

frontend-platform supports runtime configuration since 2.5.0 (see the PR
that introduced it[1], but it requires MFE cooperation.  This implements
just that: by avoiding making configuration values constant, it should
now be possible to change them after initialization.

Almost all changes here relate to the `LMS_BASE_URL` setting, which in
most places was treated as a constant.

[1] https://github.com/openedx/frontend-platform/pull/335

src/components/NavigationBar/data/api.js

@@ -2,7 +2,7 @@
 import { camelCaseObject } from '@edx/frontend-platform';
 import { getAuthenticatedHttpClient } from '@edx/frontend-platform/auth';
 
-import { API_BASE_URL } from '../../../data/constants';
+import { getApiBaseUrl } from '../../../data/constants';
 
 function normalizeCourseHomeCourseMetadata(metadata, rootSlug) {
   const data = camelCaseObject(metadata);
@@ -21,7 +21,7 @@ function normalizeCourseHomeCourseMetadata(metadata, rootSlug) {
 }
 
 export async function getCourseHomeCourseMetadata(courseId, rootSlug) {
-  const url = `${API_BASE_URL}/api/course_home/course_metadata/${courseId}`;
+  const url = `${getApiBaseUrl()}/api/course_home/course_metadata/${courseId}`;
   // don't know the context of adding timezone in url. hence omitting it
   // url = appendBrowserTimezoneToUrl(url);
   const { data } = await getAuthenticatedHttpClient().get(url);