feat(sender): add envelope draft save command and endpoint

EnvelopeGenerator.Application/Envelopes/Commands/SaveEnvelopeDraftCommand.cs

@@ -0,0 +1,39 @@
+using EnvelopeGenerator.Domain.Constants;
+using MediatR;
+
+namespace EnvelopeGenerator.Application.Envelopes.Commands;
+
+public record SaveEnvelopeDraftResultDto(int EnvelopeId, EnvelopeStatus Status);
+
+public record SaveEnvelopeDraftCommand : IRequest<SaveEnvelopeDraftResultDto>
+{
+    public int? EnvelopeId { get; init; }
+
+    public string? Title { get; init; }
+
+    public string? Message { get; init; }
+
+    public bool TFAEnabled { get; init; }
+
+    public SaveEnvelopeDraftDocumentDto? Document { get; init; }
+
+    public List<SaveEnvelopeDraftReceiverDto> Receivers { get; init; } = new();
+
+    internal int UserId { get; private set; }
+
+    public SaveEnvelopeDraftCommand WithAuth(int userId)
+    {
+        UserId = userId;
+        return this;
+    }
+}
+
+public record SaveEnvelopeDraftDocumentDto(string DataAsBase64);
+
+public record SaveEnvelopeDraftFieldDto(double X, double Y, int Page);
+
+public record SaveEnvelopeDraftReceiverDto(
+    string EmailAddress,
+    string? Name,
+    string? PhoneNumber,
+    List<SaveEnvelopeDraftFieldDto> Fields);