v.3.21.4

Improvements:

1. [LUNA-6729] Add result_url field to tasks callback in case then task is successfully done and luna-image-store is enabled. See get task notification policy.

2. [LUNA-6757] Add a detailed description to the cron field in the create tasks schedule, replace tasks schedule, get tasks schedules, get tasks schedule endpoints.

Migration:

See a migration manual.