Refactor envelope creation logic and add IEnvelopeExecutor

Updated CreateEnvelopeCommandHandler to use IEnvelopeExecutor for managing envelope creation. Introduced CreateParmas method for parameter handling in CreateEnvelopeSQL. Corrected Dapper type mapping method name and added service registration for IEnvelopeExecutor in DependencyExtensions. Refactored SQLExecutor to enhance encapsulation. Created EnvelopeExecutor class implementing IEnvelopeExecutor for dedicated envelope operations.

EnvelopeGenerator.Application/Contracts/SQLExecutor/IEnvelopeExecutor.cs

@@ -0,0 +1,19 @@
+using Dapper;
+using EnvelopeGenerator.Domain.Entities;
+
+namespace EnvelopeGenerator.Application.Contracts.SQLExecutor;
+
+/// <summary>
+/// 
+/// </summary>
+public interface IEnvelopeExecutor : ISQLExecutor
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="parameters"></param>
+    /// <param name="addUser"></param>
+    /// <param name="cancellation"></param>
+    /// <returns></returns>
+    Task<Envelope?> CreateEnvelopeAsync(DynamicParameters parameters, bool addUser = true, CancellationToken cancellation = default);
+}