Refactor envelope and user query structures

- Introduced a new `UserQuery` record to encapsulate user-related information, replacing individual fields in `EnvelopeQuery`.
- Added a `ReferenceType` property in `EnvelopeHistoryQuery` to enhance reference handling logic.
- Modified `EnvelopeQuery` to use the new `UserQuery` structure, simplifying the data model.
- Updated `HistoryController` with a new constructor and restructured the `GetReferenceTypes` method.
- Introduced `ReadEnvelopeHistoryQuery` to allow for more specific envelope history queries.
- Overall improvements enhance code structure, clarity, and querying capabilities.

EnvelopeGenerator.Application/Envelopes/EnvelopeQuery.cs

@@ -6,15 +6,18 @@ namespace EnvelopeGenerator.Application.Envelopes;
 /// Repräsentiert eine Abfrage für Umschläge.
 /// </summary>
 /// <param name="Id">Die eindeutige Kennung des Umschlags.</param>
-/// <param name="UserId">Die Kennung des Benutzers, der den Umschlag erstellt hat.</param>
-/// <param name="Username">Der Benutzername des Benutzers, der den Umschlag erstellt hat.</param>
-/// <param name="Email">Die E-Mail-Adresse des Benutzers, der den Umschlag erstellt hat.</param>
+/// <param name="User">Absender des Schreibens</param>
 /// <param name="Status">Der Status des Umschlags.</param>
 /// <param name="Uuid">Die universell eindeutige Kennung des Umschlags.</param>
 public record EnvelopeQuery(
     int? Id = null,
-    int? UserId = null,
-    string? Username = null,
-    string? Email = null,
+    UserQuery? User = null,
     int? Status = null,
-    string? Uuid = null) : IRequest;
+    string? Uuid = null) : IRequest
+{
+    public int? UserId => User?.Id;
+
+    public string? Username => User?.Username;
+
+    public string? UserEmail => User?.Username;
+};