fix: post sharing URL

When MFE uses path-based deployment (common domain for all MFEs
divided by path) - the copied link leads to 404 error.

The fix:
- construct a Post URL using MFE's `PUBLIC_PATH` env var
- works for both subdomain and subdirectory-based deployments

Note:

LMS recently started to use the discussions sidebar which has the same
button "Copy Link", but it uses its own env variable
`DISCUSSIONS_MFE_BASE_URL`

src/discussions/posts/post/Post.jsx

@@ -4,6 +4,7 @@ import PropTypes from 'prop-types';
 import { useDispatch, useSelector } from 'react-redux';
 import { useHistory, useLocation } from 'react-router-dom';
 
+import { getConfig } from '@edx/frontend-platform';
 import { injectIntl, intlShape } from '@edx/frontend-platform/i18n';
 import { Hyperlink, useToggle } from '@edx/paragon';
 
@@ -35,6 +36,9 @@ function Post({
   const { reasonCodesEnabled } = useSelector(selectModerationSettings);
   const [isDeleting, showDeleteConfirmation, hideDeleteConfirmation] = useToggle(false);
   const [isClosing, showClosePostModal, hideClosePostModal] = useToggle(false);
+
+  const postURL = new URL(`${getConfig().PUBLIC_PATH}${courseId}/posts/${post.id}`, window.location.origin);
+
   const actionHandlers = {
     [ContentActions.EDIT_CONTENT]: () => history.push({
       ...location,
@@ -50,7 +54,7 @@ function Post({
         dispatch(updateExistingThread(post.id, { closed: true }));
       }
     },
-    [ContentActions.COPY_LINK]: () => { navigator.clipboard.writeText(`${window.location.origin}/${courseId}/posts/${post.id}`); },
+    [ContentActions.COPY_LINK]: () => { navigator.clipboard.writeText(postURL.href); },
     [ContentActions.PIN]: () => dispatch(updateExistingThread(post.id, { pinned: !post.pinned })),
     [ContentActions.REPORT]: () => dispatch(updateExistingThread(post.id, { flagged: !post.abuseFlagged })),
   };