feat: Implement post search.

Related tickets:
* [TNL-8428](https://openedx.atlassian.net/browse/TNL-8428)
* [BB-4418 (OpenCraft Internal)](https://tasks.opencraft.com/browse/BB-4418)

src/discussions/posts/data/thunks.js

@@ -60,6 +60,9 @@ export function fetchThreads(courseId, {
   if (filters.status === PostsStatusFilter.UNREAD) {
     options.view = 'unread';
   }
+  if (filters.search) {
+    options.textSearch = filters.search;
+  }
   return async (dispatch) => {
     try {
       dispatch(fetchThreadsRequest({ courseId }));

src/discussions/posts/post-actions-bar/PostActionsBar.jsx

@@ -13,8 +13,9 @@ function PostActionsBar({ intl }) {
   return (
     <div className="d-flex justify-content-end py-1">
       <SearchField
-        placeholder={intl.formatMessage(messages.searchAllPosts)}
+        onClear={() => dispatch(setSearchQuery(''))}
         onSubmit={(value) => dispatch(setSearchQuery(value))}
+        placeholder={intl.formatMessage(messages.searchAllPosts)}
       />
       <Button variant="outline-primary" className="ml-2">
         {intl.formatMessage(messages.addAPost)}

src/discussions/topics/TopicsView.jsx

@@ -32,7 +32,7 @@ function TopicsView() {
         id={topicGroup.id}
         name={topicGroup.name}
         subtopics={topicGroup.children}
-        key={topicGroup.name}
+        key={topicGroup.id}
         filter={filter}
       />
     ),