Pipeline schedule mutations - GraphQL

frontend needs the ability to call pipeline schedule mutations for a project via GraphQL. More concrete info on the feature implementation can be found here app/views/projects/pipeline_schedules

Mutations needed

1. Create new schedule - !97849 (merged)
2. Play schedule - !106491 (merged)
3. Delete schedule - !97854 (merged)
4. Edit schedule - !106735 (merged)

Feel free to split these mutations up in dedicated MRs 👍