feat: adds CheckCertificateRevocation to mailkit smtp options

credit to @be4i  https://github.com/be4i/FluentEmail
closes #27

Author: JohnCampionJr

src/Senders/FluentEmail.MailKit/MailKitSender.cs

@@ -63,7 +63,9 @@ public SendResponse Send(IFluentEmail email, CancellationToken? token = null)
 
                 using (var client = _protocolLogger == null ? new SmtpClient() : new SmtpClient(_protocolLogger))
                 {
-                    if(_smtpClientOptions.ServerCertificateValidationCallback != null)
+                    client.CheckCertificateRevocation = _smtpClientOptions.CheckCertificateRevocation;
+
+                    if (_smtpClientOptions.ServerCertificateValidationCallback != null)
                     {
                         client.ServerCertificateValidationCallback = _smtpClientOptions.ServerCertificateValidationCallback;
                     }

src/Senders/FluentEmail.MailKit/SmtpClientOptions.cs

@@ -16,5 +16,8 @@ public class SmtpClientOptions
         public string MailPickupDirectory { get; set; } = string.Empty;
         public SecureSocketOptions? SocketOptions { get; set; }
         public RemoteCertificateValidationCallback ServerCertificateValidationCallback { get; set; }
+        
+        /// <inheritdoc cref="MailKit.IMailService.CheckCertificateRevocation" />
+        public bool CheckCertificateRevocation { get; set; } = true;
     }
 }