Publish an example of a Windows Store application that adds a JSON fragment extensions in Windows Terminal

The page [JSON fragment extensions in Windows Terminal](https://docs.microsoft.com/en-ca/windows/terminal/json-fragment-extensions) leads to [Create and host an app extension](https://docs.microsoft.com/en-ca/windows/uwp/launch-resume/how-to-create-an-extension). This assumes you have an app around the JSON fragment.

I think it's mandatory to have an actual example. Using *JSON fragment extensions in Windows Terminal*, a developer is unable to create a package from scratch and publish it on the Windows Store.

Ideally, someone should be able to go from [Package from the command line](https://docs.microsoft.com/en-ca/windows/msix/package/manual-packaging-root) to [JSON fragment extensions in Windows Terminal](https://docs.microsoft.com/en-ca/windows/terminal/json-fragment-extensions) and be ready to publish.

Many theme authors and their users want themes to be available in lots of places and putting a `.json` file in a specific folder is pretty easy, but it's hard for users to discover themes and to remember where their got it from. Plus, many theme authors are distributing their theme with a `.bat` or `.ps1` file to "install" it, which doesn't feel right. Being able to publish it to the Windows Store easily would solve these problems.

* https://github.com/arcticicestudio/nord/issues/123
* https://github.com/ayu-theme/ayu-colors/issues/20
* https://github.com/cocopon/iceberg.vim/issues/79
* https://github.com/dracula/windows-terminal/issues/10
* https://github.com/morhetz/gruvbox/issues/361

That example app could be in a [template repository](https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/creating-a-repository-on-github/creating-a-template-repository) so theme makers can easily have all the necessary files in place.

Start with the JSON fragment extensions in Windows Terminal page and the linked Create and host an app extension and Package from the command line guidance. Define the example app or template repository needed to take a developer from packaging through Windows Store publication. Done means the example and its publishing steps are complete and usable without an existing app.

Written by the indexing model from the issue text.