We recently moved the Web Bluetooth dashboard from a service called glitch over to GitHub pages. While not as easy to create a copy as glitch, you can fork the repository to your own GitHub account or submit Pull Requests to enhance the dashboard.
In the code, you will find an object that defines the boards with a few different options. Adding a new board is pretty easy with just a few options such as the number of NeoPixels, the color order for NeoPixels and whether it has a switch.
Adding new panels is similar to adding a new board, but there are a few more options. If you want to use one of the existing panel types, all you need to do is add a new entry to the panels and it should automatically appear, provided your board has a service and characteristic that matches what you define.