Implement a hybrid header integration approach to maximize performance and minimize re-implementation and maintenance work.

1. mock header is loaded early in the lazy phase. it only contains the basic interactive elements, but not the booking widgets and flyouts menus
2. full delta header is loaded in the delayed phase and replaces the mock header
3. user interaction events on the mock header are cached and replayed against the full header when it is loaded
4. move essential JS from the full header into the eager/lazy phase as needed on a case by case basis so martech is instrumented as early as needed