feat: E-Mail-Vorlagenverarbeitung hinzufügen

- Methode `FillTemplate` für Platzhalterersetzung hinzugefügt.
- `TemplatePlaceholderAttribute` eingeführt.
- `EmailOutService` mit Vorlagenmethoden aktualisiert.
- Unit-Tests für Vorlagenverarbeitung hinzugefügt.

DigitalData.EmailProfilerDispatcher.Application/DTOs/EmailOut/EmailOutCreateDto.cs

@@ -1,23 +1,25 @@
 namespace DigitalData.EmailProfilerDispatcher.Application.DTOs.EmailOut
 {
-    public record EmailOutCreateDto(
-        int ReminderTypeId,
-        int SendingProfile,
-        int ReferenceId,
-        string? ReferenceString,
-        int? EntityId,
-        int WfId,
-        string? WfReference,
-        string EmailAddress,
-        string EmailSubj,
-        string EmailBody,
-        string? EmailAttmt1,
-        DateTime? EmailSent,
-        string? Comment,
-        string? AddedWho,  // Default value will be 'DEFAULT', made nullable
-        string? ChangedWho,
-        DateTime? ChangedWhen,
-        DateTime? ErrorTimestamp,
-        string? ErrorMsg
-    );
-}
+	public record EmailOutCreateDto
+	{
+		public int ReminderTypeId { get; set; }
+		public int SendingProfile { get; set; }
+		public int ReferenceId { get; set; }
+		public int WfId { get; set; }
+		public string EmailAddress { get; set; }
+		public string EmailSubj { get; set; }
+		public string EmailBody { get; set; }
+		public string? ReferenceString { get; set; } = null;
+		public int? EntityId { get; set; } = null;
+		public string? WfReference { get; set; } = null;
+		public string? EmailAttmt1 { get; set; } = null;
+		public DateTime? EmailSent { get; set; } = null;
+		public string? Comment { get; set; } = null;
+		public string? AddedWho { get; set; } = "DEFAULT";
+		public string? ChangedWho { get; set; } = null;
+		public DateTime? ChangedWhen { get; set; } = null;
+		public DateTime? ErrorTimestamp { get; set; } = null;
+		public string? ErrorMsg { get; set; } = null;
+	}
+}
+