UTbot cannot setup SFTP connection with non-trivial credentials

[tyuldashev]

Description
In case user has different from utbot/utbot username and password on remote machine it is not possible configure SFTP connection and complete UTBot wizard

To Reproduce
Steps to reproduce the behavior:

1. Assume UTBbot sever user has some complicated password
2. There could be already existing proper sftp.json config file or no such one.
3. Start UTBot: QuickStart Wizard
4. On page Server Setup note that UTBot cannot connect to SFTP.
5. Try to ignore the problem and click Next button - nothing happens

Expected behavior
In case of existing sftp.json config I assume we could rely on it and don't try modify any SFTP related settings.
What's best option when there is no pre-existing configuration I don't know. Maybe just allow user to skip this wizard step.

Additional information
Even when user uses utbot/utbot credentials UTBot re-writes existing sftp.json and store password in plain test in config and rewriting other setting, which could be undesirable.

[tyuldashev]

Now it's possible to use any user/password option, but only if it's stored in plain text sftp.json config file, which could be undesirable. Entered dedicated case for that - #567