Add Worker background service to log periodic messages

Added a Worker class in EnvelopeGenerator.ServiceHost that logs an informational message every second. Registered the Worker as a hosted service in Program.cs to run alongside the web API.

EnvelopeGenerator.ServiceHost/Program.cs

@@ -5,6 +5,7 @@ var builder = WebApplication.CreateBuilder(args);
 // Add services to the container.
 
 builder.Services.AddControllers();
+builder.Services.AddHostedService<Worker>();
 
 // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
 builder.Services.AddEndpointsApiExplorer();