Sample App Design Improvements

Right now the Sample App is all structure, but we should make some functional improvements to its functionality and design.

```[tasklist]
### Essentials
- [x] Add theme selection
- [x] FlowDirection toggle
- [x] Light/Dark Theme toggle
- [ ] https://github.com/CommunityToolkit/Tooling-Windows-Submodule/issues/87
- [ ] https://github.com/CommunityToolkit/Tooling-Windows-Submodule/issues/85
```

```[tasklist]
### All components app:
- [X] Clean-up of overall documentation display, like side-panel for sample navigation and extra documentation metadata/github links, etc... (like the XAML Controls Gallery) [see comment here](https://github.com/CommunityToolkit/Labs-Windows/pull/85#discussion_r864255062)
- [X] CommunityToolkit/Tooling-Windows-Submodule#82
- [X] Create a home/landing page
- [X] Add more about information
```

```[tasklist]
### Single component app:
- [ ] Accessibility (see CommunityToolkit/Labs-Windows#86 as well)
- [X] Headings for embedded Samples/Clean-up of Sample Display/Layout _[see comment here](https://github.com/CommunityToolkit/Labs-Windows/pull/85#discussion_r864254495)_
- [ ] CommunityToolkit/Labs-Windows#67
```