[Task]: 1.0: Send current task state as a first event on "Subscribe to Task"

[ishymko]

1.0 introduced a new requirement for "Subscribe to Task" (former tasks/resubscribe) implementation:

The operation MUST return a Task object as the first event in the stream, representing the current state of the task at the time of subscription.

(source: 3.1.6. Subscribe to Task)