Log proposals and validations (#5291)

Adds detailed log messages for each validation and proposal received from the network.

src/test/csf/Peer.h

@@ -77,6 +77,12 @@ struct Peer
             return proposal_.getJson();
         }
 
+        std::string
+        render() const
+        {
+            return "";
+        }
+
     private:
         Proposal proposal_;
     };