Add a simple MAUI + Gemini chat sample

Hello, MAUI

I made a very small .NET MAUI app that shows how to connect to the Google Gemini API. The app has one page with a text box and a button. You type a question, it sends it to Gemini, and shows the answer.

The code is short and easy to follow. It uses:

`

private async Task CallGeminiAsync(string prompt)
{
string url = $"https://generativelanguage.googleapis.com/v1beta/models/gemini-2.0-flash:generateContent?key={ApiKey}";

var request = new
{
contents = new[]
{
new {
parts = new[]
{
new { text = prompt }
}
}
}
};

var json = JsonSerializer.Serialize(request);

using var http = new HttpClient();
var response = await http.PostAsync(
url,
new StringContent(json, Encoding.UTF8, "application/json")
);

string jsonResponse = await response.Content.ReadAsStringAsync();

using var doc = JsonDocument.Parse(jsonResponse);
var text = doc.RootElement
.GetProperty("candidates")[0]
.GetProperty("content")
.GetProperty("parts")[0]
.GetProperty("text")
.GetString();

return text ?? "(empty response)";
}

`

Would you be open to adding this sample to the MAUI-Samples repo? I think it could help developers see how easy it is to connect MAUI apps with AI services.

Thanks.