Add YARP reverse proxy support to API project

Integrated YARP by adding the Yarp.ReverseProxy package, including yarp.json for proxy configuration, and updating Program.cs to load and map reverse proxy routes. This enables the API to forward requests based on yarp.json settings.

EnvelopeGenerator.API/Program.cs

@@ -26,6 +26,8 @@ try
 {
     var builder = WebApplication.CreateBuilder(args);
 
+    builder.Configuration.AddJsonFile("yarp.json", optional: true, reloadOnChange: true);
+
     builder.Logging.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace);
 
     if (!builder.Environment.IsDevelopment())
@@ -39,6 +41,8 @@ try
     var deferredProvider = new DeferredServiceProvider();
 
     builder.Services.AddControllers();
+    builder.Services.AddHttpClient();
+    builder.Services.AddReverseProxy().LoadFromConfig(builder.Configuration.GetSection("ReverseProxy"));
 
     // CORS Policy
     var allowedOrigins = config.GetSection("AllowedOrigins").Get<string[]>() ??
@@ -241,6 +245,7 @@ try
     app.UseAuthentication();
     app.UseAuthorization();
 
+    app.MapReverseProxy();
     app.MapControllers();
 
     app.Run();