init: add exe name to bitcoind, bitcoin-node -version output to be able to distinguish these in tests

src/interfaces/init.h

@@ -38,6 +38,7 @@ public:
     virtual std::unique_ptr<Echo> makeEcho() { return nullptr; }
     virtual Ipc* ipc() { return nullptr; }
     virtual bool canListenIpc() { return false; }
+    virtual const char* exeName() { return nullptr; }
 };
 
 //! Return implementation of Init interface for the node process. If the argv