docs: update dotnet workshop docs (#1289)

Signed-off-by: André Silva <[email protected]>

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## This PR
This pull request updates the .NET getting started tutorial to use the
latest OpenFeature library patterns and dependency injection, improving
clarity and aligning with modern best practices. The most important
changes are grouped below:

**Dependency Injection and Library Usage Updates:**

* Added installation instructions for the `OpenFeature.Hosting` NuGet
package to support dependency injection and modern OpenFeature usage.
* Updated provider registration to use `builder.Services.AddOpenFeature`
with lambda configuration, replacing direct calls to
`Api.Instance.SetProviderAsync` for both in-memory and flagd providers.
[[1]](diffhunk://#diff-a8a7045d253a6bda66f8b29be80b12bc61d24e1b8fda49b96d4cbb117265257aL67-R84)
[[2]](diffhunk://#diff-a8a7045d253a6bda66f8b29be80b12bc61d24e1b8fda49b96d4cbb117265257aR187-R201)

**Code Modernization and API Usage:**

* Changed feature flag evaluation in route handlers to inject
`IFeatureClient` via `[FromServices]`, removing manual client
instantiation and improving testability and code clarity.
[[1]](diffhunk://#diff-a8a7045d253a6bda66f8b29be80b12bc61d24e1b8fda49b96d4cbb117265257aL105-R118)
[[2]](diffhunk://#diff-a8a7045d253a6bda66f8b29be80b12bc61d24e1b8fda49b96d4cbb117265257aL193-R213)

**Provider Integration Improvements:**

* Updated flagd provider integration to use
`OpenFeature.Contrib.Providers.Flagd.DependencyInjection` and the
`.AddFlagdProvider()` extension for simpler configuration.
[[1]](diffhunk://#diff-a8a7045d253a6bda66f8b29be80b12bc61d24e1b8fda49b96d4cbb117265257aL165-R174)
[[2]](diffhunk://#diff-a8a7045d253a6bda66f8b29be80b12bc61d24e1b8fda49b96d4cbb117265257aR187-R201)

---------

Signed-off-by: André Silva <[email protected]>

Author: askpt

docs/tutorials/getting-started/dotnet.mdx

@@ -45,6 +45,7 @@ With NuGet you can install the latest [OpenFeature](https://www.nuget.org/packag
 
 ```shell
 dotnet add package OpenFeature
+dotnet add package OpenFeature.Hosting
 ```
 
 ### Step 3: Add code
@@ -54,7 +55,9 @@ Open a code editor and add the C# code below to the Program.cs.
 
 ```csharp
 // diff-add-block-start
+using Microsoft.AspNetCore.Mvc;
 using OpenFeature;
+using OpenFeature.Hosting.Providers.Memory;
 using OpenFeature.Providers.Memory;
 // diff-add-block-end
 
@@ -64,13 +67,23 @@ var builder = WebApplication.CreateBuilder(args);
 // Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
 builder.Services.AddOpenApi();
 
-var app = builder.Build();
-
 // diff-add-block-start
 // Register your feature flag provider
-await Api.Instance.SetProviderAsync(new InMemoryProvider());
+builder.Services.AddOpenFeature(featureBuilder =>
+{
+    featureBuilder
+        .AddInMemoryProvider(_ => new Dictionary<string, Flag>()
+        {
+            {
+                "welcome-message", new Flag<bool>(
+                    new Dictionary<string, bool> { { "show", true }, { "hide", false } }, "show")
+            }
+        });
+});
 // diff-add-block-end
 
+var app = builder.Build();
+
 // Configure the HTTP request pipeline.
 if (app.Environment.IsDevelopment())
 {
@@ -102,11 +115,9 @@ app.MapGet("/weatherforecast", () =>
 .WithName("GetWeatherForecast");
 //diff-remove-block-end
 //diff-add-block-start
-app.MapGet("/hello", async () =>
+app.MapGet("/hello", async ([FromServices] IFeatureClient featureClient) =>
 {
-    var client = Api.Instance.GetClient();
-
-    if (await client.GetBooleanValueAsync("welcome-message", false))
+    if (await featureClient.GetBooleanValueAsync("welcome-message", false))
     {
         return "Hello, welcome to this OpenFeature-enabled website!";
     }
@@ -160,11 +171,15 @@ Finally, let's add the required code change to enable the flagd provider in our
 
 ```csharp
 
+using Microsoft.AspNetCore.Mvc;
 using OpenFeature;
-//diff-add
-using OpenFeature.Contrib.Providers.Flagd
-//diff-remove
+//diff-add-block-start
+using OpenFeature.DependencyInjection.Providers.Flagd;
+//diff-add-block-end
+//diff-remove-block-start
 using OpenFeature.Providers.Memory;
+using OpenFeature.Hosting.Providers.Memory;
+//diff-remove-block-end
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -175,12 +190,20 @@ builder.Services.AddOpenApi();
 var app = builder.Build();
 
 // Register your feature flag provider
-//diff-remove
-await Api.Instance.SetProviderAsync(new InMemoryProvider());
+builder.Services.AddOpenFeature(featureBuilder =>
+{
+    featureBuilder
+        .AddInMemoryProvider(_ => new Dictionary<string, Flag>()
+        {
+            {
+                "welcome-message", new Flag<bool>(
+                    new Dictionary<string, bool> { { "show", true }, { "hide", false } }, "show")
+            }
+        });
 //diff-add-block-start
-var flagdProvider = new FlagdProvider(new Uri("http://localhost:8013"));
-await Api.Instance.SetProviderAsync(flagdProvider);
+        .AddFlagdProvider();
 //diff-add-block-end
+});
 
 // Configure the HTTP request pipeline.
 if (app.Environment.IsDevelopment())
@@ -190,11 +213,9 @@ if (app.Environment.IsDevelopment())
 
 app.UseHttpsRedirection();
 
-app.MapGet("/hello", async () =>
+app.MapGet("/hello", async ([FromServices] IFeatureClient featureClient) =>
 {
-    var client = Api.Instance.GetClient();
-
-    if (await client.GetBooleanValueAsync("welcome-message", false))
+    if (await featureClient.GetBooleanValueAsync("welcome-message", false))
     {
         return "Hello, welcome to this OpenFeature-enabled website!";
     }