Refactor ExceptionHandlingMiddleware and update dependencies

Rewrote the `ExceptionHandlingMiddleware` class to improve structure and functionality, changing its namespace to `DigitalData.Core.Exceptions`. Updated the constructor to support a nullable logger and implemented null-conditional logging for unhandled exceptions. Added new package references in `DigitalData.Core.Exceptions.csproj` for `Microsoft.AspNetCore.Http.Abstractions` and `Microsoft.Extensions.Logging.Abstractions`. Introduced a new `DependencyInjection` class to register the middleware in the application's pipeline.

DigitalData.Core.Exceptions/DependencyInjection.cs

@@ -0,0 +1,12 @@
+using Microsoft.AspNetCore.Builder;
+
+namespace DigitalData.Core.Exceptions;
+
+public static class DependencyInjection
+{
+    public static IApplicationBuilder UseExceptionHandlingMiddleware(this IApplicationBuilder app)
+    {
+        app.UseMiddleware<ExceptionHandlingMiddleware>();
+        return app;
+    }
+}