Include in MAUI samples browser (#281)

## Purpose
Add the dotnet-maui product to the README metadata so that the sample
shows up in the MAUI samples browser.

## Does this introduce a breaking change?
<!-- Mark one with an "x". -->
```
[ ] Yes
[x] No
```

## Pull Request Type
What kind of change does this Pull Request introduce?

<!-- Please check the one that applies to this PR using "x". -->
```
[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[x] Documentation content changes
[ ] Other... Please describe:
```

## How to Test
*  Get the code

```
git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install
```

* Test the code
<!-- Add steps to run the tests suite and/or manually test -->
```
```

## What to Check
Verify that the following are valid
* ...

## Other Information
<!-- Add any other helpful information that may be needed here. -->

Co-authored-by: Bret Johnson <[email protected]>

Author: Bret Johnson

README.md

@@ -15,6 +15,7 @@ products:
 - blazor
 - defender-for-cloud
 - azure-monitor
+- dotnet-maui
 urlFragment: azure-search-openai-demo-csharp
 name: ChatGPT + Enterprise data (csharp)
 description: A csharp sample app that chats with your data using OpenAI and AI Search.