MM-33544 is_following prop in getPosts API methods (#17093)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

store/storetest/thread_store.go

@@ -70,7 +70,7 @@ func testThreadStorePopulation(t *testing.T, ss store.Store) {
 
 		newPosts, errIdx, err3 := ss.Post().SaveMultiple([]*model.Post{&o2, &o3, &o4})
 
-		olist, _ := ss.Post().Get(context.Background(), otmp.Id, true, false, false)
+		olist, _ := ss.Post().Get(context.Background(), otmp.Id, true, false, false, "")
 		o1 := olist.Posts[olist.Order[0]]
 
 		newPosts = append([]*model.Post{o1}, newPosts...)