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

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

app/plugin_api.go

@@ -574,7 +574,7 @@ func (api *PluginAPI) DeletePost(postID string) *model.AppError {
 }
 
 func (api *PluginAPI) GetPostThread(postID string) (*model.PostList, *model.AppError) {
-	return api.app.GetPostThread(postID, false, false, false)
+	return api.app.GetPostThread(postID, false, false, false, "")
 }
 
 func (api *PluginAPI) GetPost(postID string) (*model.Post, *model.AppError) {