Add AddReceiver method and refactor SQL classes

Introduced a new `AddReceiver` method in the `Extension` class to facilitate adding a receiver to an envelope. This method includes parameters for `envelope_uuid`, `emailAdress`, `salutation`, and an optional `phone`, along with XML documentation for clarity.

Removed the `EnvelopeReceiverCreateReadSQL` class and added the `EnvelopeReceiverAddReadSQL` class, which defines the SQL command for adding a receiver. The new class also includes XML documentation comments for better understanding.

EnvelopeGenerator.Application/SQL/EnvelopeReceiverAddReadSQL.cs

@@ -0,0 +1,33 @@
+using EnvelopeGenerator.Application.Contracts.SQLExecutor;
+using EnvelopeGenerator.Domain.Entities;
+
+namespace EnvelopeGenerator.Application.SQL;
+
+/// <summary>
+/// 
+/// </summary>
+public class EnvelopeReceiverAddReadSQL : ISQL<Envelope>
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    public string Raw => @"
+		USE [DD_ECM]
+		GO
+
+		DECLARE	@OUT_RECEIVER_ID int
+
+		DECLARE	@ENV_UID varchar(36) = @ENV_UID
+
+		EXEC	[dbo].[PRSIG_API_CREATE_RECEIVER]
+				@ENV_UID = @ENV_UID,
+				@EMAIL_ADRESS = @EMAIL_ADRESS ,
+				@SALUTATION = @SALUTATION,
+				@PHONE = @PHONE,
+				@OUT_RECEIVER_ID = @OUT_RECEIVER_ID OUTPUT
+
+		SELECT TOP(1) *
+		FROM TBSIG_ENVELOPE_RECEIVER
+		WHERE [GUID] = @OUT_RECEIVER_ID;
+	";
+}