[CLI] binary level integration tests

[billy1624]

Motivation

Currently, we don't have tests on CLI binary for example running sea-orm-cli generate entity --options --flags then validate the behaviour of the command.

Without it, naive mistakes will be made, such as #1250.

Proposed Solutions

The CLI now has two main functionality, generate entity files and run migration. We could test both at the same time. Strat with running migration, then follow by generating entity files against the database schema with the applied migrations.