[FEAT] Update dgeni to only display HTML file in design example

[xelaint]

:bulb: Feature request

Feature Name

Update dgeni to only display HTML file in design example

The Desired Behavior

DesignLandCodeExample should only display the HTML file of a design example. Component, module, and sass files will be moved to StackBlitz (#2066)

Your Use Case

As a designer, I'd like to simplify the UI of code preview.

Prior Work

Environment

Daffodil version: X.Y.Z
Angular version: X.Y.Z 

 
For Tooling issues:
- Node version: XX  
- Platform:  

Others: