Add DocResult property and update EnvelopeController

- Introduced a new `DocResult` property in `EnvelopeDto.cs` and `Envelope.cs` for handling binary data.
- Rearranged properties in `EnvelopeDto.cs` for better organization.
- Modified `EnvelopeController` to return a collection of envelopes instead of a single envelope.

EnvelopeGenerator.GeneratorAPI/Controllers/EnvelopeController.cs

@@ -76,7 +76,7 @@ public class EnvelopeController : ControllerBase
                         if (envelope.Uuid is string uuid)
                             envelopes = envelopes.Where(e => e.Uuid == uuid);
 
-                        return Ok(envelope);
+                        return Ok(envelopes);
                     },
                     Fail: IActionResult (msg, ntc) =>
                     {