Currently, our core and side module dependent on each others. and will cause
cycle import in our codebase, especially in issue #10905, we try to refactor
to solve this problem.

This patch do the following change:

* Rename module `side` to `models`
* Move `core/base` and `core/sidebase` to dir `modules`
* Move `configuration` and `default_config.yaml` to the root of pydolphinscheduler