Added high dynamic range (HDR) sandcastle example

[IanLilleyT]

For #8102

Added a toggle for HDR in sandcastle. Includes a dazzling view of the grand canyon and a milk truck.

[cesium-concierge]

Thanks for the pull request @IanLilleyT!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[lilleyse]

Can you rename the example to High Dynamic Range?

[lilleyse]

@IanLilleyT there are some eslint errors that caused CI to fail.

[lilleyse]

Looks good, thanks @IanLilleyT