[Model discovery] Need to force to exit when running lb4 discover command

[dhmlau]

Description / Steps to reproduce / Feature proposal

When running lb4 discover as below, the prompt never returns, and I need to press Ctrl+C to exit. The models are being created properly, but I need to kill the process in order to get the prompt back.

   $ lb4 discover --schema testdb
   ? Select the connector to discover ds
   ? Select the models which to discover address, customer
     create src/models/address.model.ts
     create src/models/customer.model.ts
     update src/models/index.ts
     update src/models/index.ts

   Discover address.model.ts,customer.model.ts was created in src/models/

Acceptance Criteria

• Make sure to close all open datasource connections i.e. call datasource.disconnect()
• Create/Update test(s) accordingly (try to capture/reproduce bug in tests)
• Test against real live database (pick one SQL and NoSQL like MySQL/Mongo)

I'm using MySQL as the datasource, not sure if it matters.

[dhmlau]

cc @marvinirwin

[bajtos]

I suspect the connector is keeping a pool of connections opened and these connections are blocking Node.js from exiting.

I think we should improve packages/cli/generators/discover/index.js to call await this.artifactInfo.dataSource.disconnect() after we have fetched all data from the database.