Add global exception handling middleware

Introduce `ExceptionHandlingMiddleware` to capture and log exceptions globally in the application. This middleware returns appropriate JSON error responses based on specific exception types, such as `BadRequestException` and `NotFoundException`. The middleware is registered in `Program.cs` to ensure it processes all HTTP requests.

EnvelopeGenerator.GeneratorAPI/Program.cs

@@ -15,6 +15,7 @@ using EnvelopeGenerator.GeneratorAPI.Models;
 using Microsoft.AspNetCore.Authentication.JwtBearer;
 using Microsoft.IdentityModel.Tokens;
 using DigitalData.Core.Abstractions.Security.Extensions;
+using EnvelopeGenerator.GeneratorAPI.Middleware;
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -169,6 +170,8 @@ var app = builder.Build();
 
 deferredProvider.Factory = () => app.Services;
 
+app.UseMiddleware<ExceptionHandlingMiddleware>();
+
 app.MapOpenApi();
 
 // Configure the HTTP request pipeline.