Implement jwks endpoint and add test for it.

This also let to some improvements/cleanups of the other tests and fixtures.

IdentityShroud.Core/Model/Realm.cs

@@ -1,5 +1,7 @@
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
+using IdentityShroud.Core.Security;
+using Microsoft.EntityFrameworkCore;
 
 namespace IdentityShroud.Core.Model;
 
@@ -19,4 +21,10 @@ public class Realm
     public List<Client> Clients { get; init; } = [];
 
     public List<Key> Keys { get; init; } = [];
-}
+
+    /// <summary>
+    /// Can be overriden per client
+    /// </summary>
+    public string DefaultSignatureAlgorithm { get; set; } = JsonWebAlgorithm.RS256;
+    
+}