Add AddEnvelopeReceiver method and SQL class

Introduces the `AddEnvelopeReceiver` method in the `Extension` class to add envelope receivers with parameters for UUID, email, salutation, and optional phone.

Also adds the `EnvelopeReceiverAddReadSQL` class implementing `ISQL<Envelope>`, containing a SQL query to create a new receiver using the stored procedure `PRSIG_API_CREATE_RECEIVER`.

Includes XML documentation for improved code readability and maintainability.

EnvelopeGenerator.Application/Contracts/SQLExecutor/Extension.cs

@@ -55,4 +55,26 @@ public static class Extension
 
         return await executor.CreateEnvelopeAsync(parameters, cancellation: cancellation);
     }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="executor"></param>
+    /// <param name="envelope_uuid"></param>
+    /// <param name="emailAdress"></param>
+    /// <param name="salutation"></param>
+    /// <param name="phone"></param>
+    /// <param name="cancellation"></param>
+    /// <returns></returns>
+    public static async Task<EnvelopeReceiver?> AddEnvelopeReceiver(this ISQLExecutor executor, string envelope_uuid, string emailAdress, string salutation, string? phone = null, CancellationToken cancellation = default)
+    {
+        var parameters = new DynamicParameters();
+        parameters.Add("@ENV_UID", envelope_uuid);
+        parameters.Add("@EMAIL_ADRESS", emailAdress);
+        parameters.Add("@SALUTATION", salutation);
+        parameters.Add("@PHONE", phone);
+
+        var envelopeReceivers = await executor.Execute<EnvelopeReceiver, EnvelopeReceiverAddReadSQL>(parameters, cancellation);
+        return envelopeReceivers.FirstOrDefault();
+    }
 }