Added a form for entering a passphrase for a private ssh key and the corresponding logic for processing a private key

client/core/defs.h

@@ -13,6 +13,7 @@ struct ServerCredentials
     QString hostName;
     QString userName;
     QString password;
+    QString decryptedPrivateKey;
     int port = 22;
 
     bool isValid() const { return !hostName.isEmpty() && !userName.isEmpty() && !password.isEmpty() && port > 0; }