postgres - add data source, make run demo

[reywang18]

I choose postgresql db; which installed locally.

The default db for postgresql is same as user ID.
And demo only asks about host/port/user/password, no DB name setting.
Can it be more flexible here?

The connection target DEFAULT initiates a connection to the default database under the default user name.

[mouadhkaabachi]

Hi reywang18,
right now , to add cube from db, you need first to ensure that the connection is successfully established with your db engine, and then you choose the target db

I will add a demo postgres dump to the repo, and you can test with it