Add envelope creation functionality and SQL integration

- Updated `EnvelopeGenerator.Application.csproj` to include `Microsoft.Data.SqlClient` package.
- Refactored `CreateEnvelopeReceiverCommand` to inherit from `CreateEnvelopeCommand`.
- Enhanced `CreateEnvelopeSQL` with a SQL script for envelope creation.
- Introduced `CreateEnvelopeCommand` to encapsulate envelope creation data.
- Added `CreateEnvelopeCommandHandler` to process commands and interact with the database.
- Created `CreateEnvelopeResponse` class for handling responses from envelope creation.

EnvelopeGenerator.Application/EnvelopeReceivers/Commands/Create/CreateEnvelopeReceiverCommand.cs

@@ -1,4 +1,5 @@
-using MediatR;
+using EnvelopeGenerator.Application.Envelopes.Commands;
+using MediatR;
 using System.ComponentModel.DataAnnotations;
 
 namespace EnvelopeGenerator.Application.EnvelopeReceivers.Commands.Create;
@@ -17,7 +18,7 @@ public record CreateEnvelopeReceiverCommand(
     [Required] DocumentCreateCommand Document,
     [Required] IEnumerable<ReceiverGetOrCreateCommand> Receivers,
     bool TFAEnabled = false
-    ) : IRequest;
+    ) : CreateEnvelopeCommand(Title, Message, TFAEnabled), IRequest;
 
 #region DTOs
 /// <summary>