Introduce `SyncEvent` channel in current stream management system, utilize to implement `SyncEventStream.EventStream` on translation shim type.

[timwu20]

Issue summary

• blocked by Support detection of EOF and ErrClosedPipe in current network stream #4802
• Create SyncEvent channel in translation shim which captures SyncEvent instances.
• These are the events that should be emitted from the sync engine.

Implementation details

• Calls to EventStream is essentially registering a subscriber to all SyncEvents.
• SyncEvent instances must be copied and sent to all subscribers

Other information and links

Acceptance criteria

[] SyncEvent subscribers should be able to subscribe to SyncEvents by calling EventStream.
[] 70% unit test coverage on introduced methods and functionality.