Enhance query criteria and add partial email matching

- Added `[NotMapped]` attribute to `HasAnyCriteria` in `ReceiverQueryBase` to exclude it from database mapping.
- Made `HasAnyCriteria` in `ReceiverQueryBase` virtual for overriding.
- Introduced `EmailAddressSearch` in `ReadReceiverQuery` for partial email matching.
- Overrode `HasAnyCriteria` in `ReadReceiverQuery` to include `EmailAddressSearch`.
- Updated `ReadReceiverQueryHandler` to support partial email matching using `EF.Functions.Like`.

EnvelopeGenerator.Application/Receivers/Queries/ReadReceiverQuery.cs

@@ -5,6 +5,7 @@ using EnvelopeGenerator.Application.Common.Query;
 using MediatR;
 using EnvelopeGenerator.Domain.Entities;
 using Microsoft.EntityFrameworkCore;
+using System.ComponentModel.DataAnnotations.Schema;
 
 namespace EnvelopeGenerator.Application.Receivers.Queries;
 
@@ -12,7 +13,24 @@ namespace EnvelopeGenerator.Application.Receivers.Queries;
 /// Stellt eine Abfrage dar, um die Details eines Empfängers zu lesen.
 /// um spezifische Informationen über einen Empfänger abzurufen.
 /// </summary>
-public record ReadReceiverQuery : ReceiverQueryBase, IRequest<IEnumerable<ReceiverDto>>;
+public record ReadReceiverQuery : ReceiverQueryBase, IRequest<IEnumerable<ReceiverDto>>
+{
+    /// <summary>
+    /// Suchbegriff für eine teilweise Übereinstimmung in der E-Mail Adresse des Empfängers
+    /// </summary>
+    public virtual string? EmailAddressSearch { get; set; }
+
+    /// <summary>
+    /// Checks whether any of the specified query criteria have a value.
+    /// </summary>
+    /// <remarks>
+    /// This property returns <c>true</c> if at least one of the fields 
+    /// <see cref="ReceiverQueryBase.Id"/>, <see cref="ReceiverQueryBase.EmailAddress"/>, <see cref="EmailAddressSearch"/>, or <see cref="ReceiverQueryBase.Signature"/> is not null.
+    /// <para>Usage example: The query can be executed only if at least one criterion is specified.</para>
+    /// </remarks>
+    [NotMapped]
+    public override bool HasAnyCriteria => EmailAddressSearch is not null || base.HasAnyCriteria;
+}
 
 /// <summary>
 /// 
@@ -53,6 +71,11 @@ public class ReadReceiverQueryHandler : IRequestHandler<ReadReceiverQuery, IEnum
             query = query.Where(r => r.EmailAddress == email);
         }
 
+        if (!string.IsNullOrWhiteSpace(request.EmailAddressSearch))
+        {
+            query = query.Where(r => EF.Functions.Like(r.EmailAddress, $"%{request.EmailAddressSearch}%"));
+        }
+
         if (request.Signature is string signature)
         {
             query = query.Where(r => r.Signature == signature);