* [ci] Add coverage check in CI
* Coverage add dependent
* Install pydolphinscheduler before run coverage
* Up test coverage to 87% and down threshold to 85%
* Fix code style
* Add doc about coverage
* [python] Add parameter schedule for process definition
* Rebase and fix some code style
* May schedule work on both string and datetime
* Fix flaky test
* Add comment about freeze time
* Add edge test for schedule_json with None schedule
* Fix test function name
* Fix rebase error
Jiajie Zhong