Add DTOs and tests for placeholder replacement

Added new record types `CreateEnvelopeDocumentDto`, `CreateEnvelopeFieldDto`, and `CreateEnvelopeReceiverDto` with XML documentation in `CreateEnvelopeCommand.cs`. Marked `ConfigService` as obsolete in `CreateEnvelopeCommandHandler.cs`. Modified `CertificationType` usage in `Fake.cs` to use the enum directly. Updated `EnvelopeGenerator.Tests.csproj` with a new project reference and compile directives. Introduced `MailTemplatePlaceholderDbTests` and `ReplacePlaceholderExtensionsTests` to verify placeholder replacement functionality. Added supporting model classes for testing. These changes improve code functionality and test coverage.

EnvelopeGenerator.Application/Envelopes/Commands/CreateEnvelopeCommand.cs

@@ -130,10 +130,27 @@ public record CreateEnvelopeCommand : IRequest<EnvelopeDto?>
     public bool UseSQLExecutor { get; set; } = true;
 }
 
+/// <summary>
+/// 
+/// </summary>
+/// <param name="DataAsBase64"></param>
 public record CreateEnvelopeDocumentDto(string DataAsBase64);
 
+/// <summary>
+/// 
+/// </summary>
+/// <param name="X"></param>
+/// <param name="Y"></param>
+/// <param name="Page"></param>
 public record CreateEnvelopeFieldDto(double X, double Y, int Page);
 
+/// <summary>
+/// 
+/// </summary>
+/// <param name="EmailAddress"></param>
+/// <param name="Name"></param>
+/// <param name="PhoneNumber"></param>
+/// <param name="Fields"></param>
 public record CreateEnvelopeReceiverDto(
     string EmailAddress,
     string? Name,

EnvelopeGenerator.Application/Envelopes/Commands/CreateEnvelopeCommandHandler.cs

@@ -49,6 +49,7 @@ public class CreateEnvelopeCommandHandler : IRequestHandler<CreateEnvelopeComman
 
     private SignatureFieldParams SignatureFieldParams => _provider.GetRequiredService<IOptionsMonitor<SignatureFieldParams>>().CurrentValue;
 
+    [Obsolete("Use IConfigService instead.")]
     private IConfigService ConfigService => _provider.GetRequiredService<IConfigService>();
 
     private IMediator Mediator => _provider.GetRequiredService<IMediator>();