refactor: Receiver-Service in CRUD-Service umgewandelt und DTOs aktualisiert

- Receiver-Service von einfachem CRUD zu generischem CRUD-Service umgewandelt.
- `ReceiverDto` in `ReceiverReadDto` umbenannt.
- Neues `ReceiverCreateDto` mit automatischer SHA-256-Signaturerstellung und aktuellem Zeitstempel erstellt.
- Leeres `ReceiverUpdateDto` für zukünftige Updates hinzugefügt.

EnvelopeGenerator.Application/DTOs/Receiver/ReceiverCreateDto.cs

@@ -0,0 +1,20 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace EnvelopeGenerator.Application.DTOs.Receiver
+{
+    public record ReceiverCreateDto(string EmailAddress)
+    {
+        public string Signature => sha256HexOfMail.Value;
+
+        private readonly Lazy<string> sha256HexOfMail = new(() =>
+        {
+            var bytes_arr = Encoding.UTF8.GetBytes(EmailAddress.ToUpper());
+            var hash_arr = SHA256.HashData(bytes_arr);
+            var hexa_str = BitConverter.ToString(hash_arr);
+            return hexa_str.Replace("-", string.Empty);
+        });
+
+        public DateTime AddedWhen { get; } = DateTime.Now;
+    };
+}

EnvelopeGenerator.Application/DTOs/Receiver/ReceiverReadDto.cs

@@ -0,0 +1,11 @@
+using DigitalData.Core.DTO;
+
+namespace EnvelopeGenerator.Application.DTOs.Receiver
+{
+    public record ReceiverReadDto(
+        int Id,
+        string EmailAddress,
+        string Signature,
+        DateTime AddedWhen
+        ) : BaseDTO<int>(Id);
+}

EnvelopeGenerator.Application/DTOs/Receiver/ReceiverUpdateDto.cs

@@ -0,0 +1,4 @@
+namespace EnvelopeGenerator.Application.DTOs.Receiver
+{
+    public record ReceiverUpdateDto();
+}