qtlicensetool.exe update existing qtlicd.ini

As a user
I want that the changes I have done in qtlicd.ini file are kept during updates
So that the settings I need to use are preserved

Currently there is no practical way in Qt Installer to merge the user modified values into new version of the qtlicd.ini file. 

Instead, this probably should be done in the qtlicensetool.exe itself via a command line option. This way we also decouple the dependency to Qt installer.

qtlicensetool.exe --merge-settings --source <source qtlicd.ini> --dest <dest qtlicd.ini> --force-overwrite key1=value1 key2=value2

If the --dest file is missing, then it will be provisioned with the values from --source.

If the --source is missing, then default values will be used for --dest

If --force-overwrite is given then the --dest will be overridden with the value from --source, even if the --dest already contains the same key