Refactor namespaces for SignCommand and behaviors

Updated namespaces from `Signature` to `Signatures` for consistency and clarity across the application. Simplified pipeline behavior registrations in `DependencyInjection.cs` by using shorter references. Added `Microsoft.Extensions.Configuration` to `DependencyInjection.cs` to support configuration functionality. Ensured all references to `SignCommand` and related behaviors align with the new namespace structure.

EnvelopeGenerator.Application/Signatures/Behaviors/HistoryBehavior.cs

@@ -0,0 +1,47 @@
+using EnvelopeGenerator.Application.Common.Extensions;
+using EnvelopeGenerator.Application.Histories.Commands;
+using EnvelopeGenerator.Application.Signatures.Commands;
+using EnvelopeGenerator.Domain.Constants;
+using MediatR;
+
+namespace EnvelopeGenerator.Application.Signatures.Behaviors;
+
+/// <summary>
+/// Pipeline behavior that records history.
+/// Executes third in the signing process.
+/// </summary>
+public class HistoryBehavior : IPipelineBehavior<SignCommand, Unit>
+{
+    private readonly ISender _sender;
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="sender"></param>
+    public HistoryBehavior(ISender sender)
+    {
+        _sender = sender;
+    }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="request"></param>
+    /// <param name="next"></param>
+    /// <param name="cancellationToken"></param>
+    /// <returns></returns>
+    public async Task<Unit> Handle(SignCommand request, RequestHandlerDelegate<Unit> next, CancellationToken cancellationToken)
+    {
+        if (request.EnvelopeReceiver.Receiver is null)
+            throw new InvalidOperationException($"Receiver information is missing in the notification. SignCommand:\n {request.ToJson(Format.Json.ForDiagnostics)}");
+
+        await _sender.Send(new CreateHistoryCommand()
+        {
+            EnvelopeId = request.EnvelopeReceiver.EnvelopeId,
+            UserReference = request.EnvelopeReceiver.Receiver.EmailAddress,
+            Status = EnvelopeStatus.DocumentSigned,
+        }, cancellationToken);
+
+        return await next();
+    }
+}