use 'is_rootcanal_signed' from the config

Summary:
'is_rootcanal_signed' is set in the config based on who issues the given cert.
but this field in not used anywhere in the proxygen code, yet.

let's read this field to set 'isProdCASigned'. it'll be used to decide if the
cert can be fetched directly from ProdCA.

"ProdCA" is used because its the preferred name vs "rootcanal".

Reviewed By: zalecodez

Differential Revision: D51176576

fbshipit-source-id: 5827b2902d1a7b9d08067a14d723df78cef5cc0d

wangle/ssl/SSLContextConfig.h

@@ -149,6 +149,9 @@ struct SSLContextConfig {
   // Load cert-key pairs corresponding to these domains
   std::vector<std::string> domains;
 
+  // If true, the certs for this domain is signed by our internal CA
+  bool isProdCASigned{false};
+
   // A namespace to use for sessions generated from this context so that
   // they will not be shared between other sessions generated from the
   // same context. If not specified the vip name will be used by default