I'm working on a migration project for a client, they have a lot of custom components that they've relied on in the past for site construction that they won't have access to after the migration. Among those is their main site navigation, a header component that uses mega menus for site navigation. I want to know what options are available for recreating that functionality in the modern AEM landscape. Are there any good tutorials for how to writer a mega menu component? Are there any vendors that sell or license these sort of components?