feature
- add event handler for dijob, and mark job as Created when job submitted(https://github.com/opendilab/DI-orchestrator/pull/13)
- mark collector and learner as optional, only coordinator is required(https://github.com/opendilab/DI-orchestrator/pull/13/commits/653e64af01ec7752b08d4bf8381738d566fca224)
- mark job Failed when the submitted job is incorrect(https://github.com/opendilab/DI-orchestrator/pull/13/commits/bea840a5eee3508be18b53b325168a5647daff94), but it's hard to test since client-go reflector decodes DIJob strictly, we have no chance to handle DIJob add event when incorrect job submitted