821 internal error after canceling scheduled execution and starting with saved configuration

[zaychenko-sergei]

Description

Closes: #821

High-level handling for aborting flows at different stages of processing + tests. Detecting concurrent modification errors for task & flow event stores, and reporting those as internal errors.

Checklist before requesting a review

• [x] Unit and integration tests added
• [x] Compatibility:
  • [x] Network APIs: ✅
  • [x] Workspace layout and metadata: ✅
  • [x] Configuration: ✅
  • [x] Container images: ✅
• [ ] Documentation:
  • [x] Changelog: ✅
  • [ ] Public documentation: ✅
• [ ] Downstream effects:
  • [ ] kamu-node: ✅