https: New option to validate, CertPubKey

This option validates signature of remote certificate.
It is always possible that malicious actor might put MITM
node and obtain his own certificate.
In fact such attack already happened, one of well documented cases:
https://notes.valdikss.org.ru/jabber.ru-mitm/
The only way to detect such malicious intent is by validating
certificate public key.

Signed-off-by: Denys Fedoryshchenko <denys.f@collabora.com>

simplomon.hh

@@ -239,6 +239,7 @@ private:
 
   std::string d_method;
   std::string d_agent="Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36";
+  std::string d_cert_pubkey;
 };