create dbvis_add_db_admin.rb

Dbvisulaizer offers a command line functionality to execute SQL pre-configured databases (With GUI).
The remote database can be accessed from the command line without the need to authenticate.
The module abuses this functionality to create an administrator in the database if DB user rights allow it.
In Windows, you can also try ```client.fs.file.search``` (or session.fs.file.search), which is the same method the meterpreter command "search" uses. An example of using the search method can be found here:
https://github.com/rapid7/metasploit-framework/blob/master/lib/rex/post/meterpreter/ui/console/command_dispatcher/stdapi/fs.rb#L102