Implement jwks endpoint and add test for it.

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

IdentityShroud.Core.Tests/UnitTest1.cs

@@ -95,14 +95,5 @@ public static class RsaKeyLoader
         string pemContent = System.IO.File.ReadAllText(filePath);
         return LoadFromPem(pemContent);
     }
-    
-    /// <summary>
-    /// Load RSA private key from PKCS#8 format
-    /// </summary>
-    public static RSA LoadFromPkcs8(byte[] pkcs8Key)
-    {
-        var rsa = RSA.Create();
-        rsa.ImportPkcs8PrivateKey(pkcs8Key, out _);
-        return rsa;
-    }
+   
 }