Refactor “Get started” menu at desktop

This is a followup from 📌 Recreate main menu Active

The "Get started" menu at desktop needs to be refactored. It's currently a hover menu, while the rest of the header is click only.

• Menu should be activated on click with a disclosure button
• Button should close other items when clicked, and should close when other items are clicked
• Menu should be styled like a link button. Note there's discussion around the confusion of this, and will likely be changed in the future.
• Menu should use SDC/BEM/Modern CSS/Best practices.