feat(core): IUnique-Schnittstelle hinzufügen und Core.Infrastructure aktualisieren

- `IUnique`-Schnittstelle zu allen Entitäten im Domain-Projekt hinzugefügt.
- `Core.Infrastructure` auf Version 2.0.0.0 im Infrastructure-Layer aktualisiert.
- Domain-Projekt mit `Core.Abstraction` für verbesserte Abstraktion erweitert.

EnvelopeGenerator.Domain/Entities/Envelope.cs

@@ -1,12 +1,12 @@
-using EnvelopeGenerator.Common;
-using EnvelopeGenerator.Common.My.Resources;
+using DigitalData.Core.Abstractions;
+using EnvelopeGenerator.Common;
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
 
 namespace EnvelopeGenerator.Domain.Entities
 {
     [Table("TBSIG_ENVELOPE", Schema = "dbo")]
-    public class Envelope
+    public class Envelope : IUnique<int>
     {
         [Key]
         [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
@@ -26,11 +26,11 @@ namespace EnvelopeGenerator.Domain.Entities
 
         [Required]
         [Column("ENVELOPE_UUID", TypeName = "nvarchar(36)")]
-        public string Uuid { get; set; }
+        public required string Uuid { get; init; }
 
         [Required]
         [Column("MESSAGE", TypeName = "nvarchar(max)")]
-        public string Message { get; set; }
+        public string? Message { get; set; }
 
         [Column("EXPIRES_WHEN", TypeName = "datetime")]
         public DateTime? ExpiresWhen { get; set; }
@@ -46,13 +46,13 @@ namespace EnvelopeGenerator.Domain.Entities
         public DateTime? ChangedWhen { get; set; }
 
         [Column("TITLE", TypeName = "nvarchar(128)")]
-        public string Title { get; set; }
+        public string? Title { get; set; }
 
         [Column("CONTRACT_TYPE")]
         public int? ContractType { get; set; }
 
         [Column("LANGUAGE", TypeName = "nvarchar(5)")]
-        public string Language { get; set; }
+        public required string Language { get; set; }
 
         [Column("SEND_REMINDER_EMAILS")]
         public bool? SendReminderEmails { get; set; }