serve response via ack for sync and sync-serve

[vigith]

No description provided.

[BulkBeing]

I don't think we need to handle the /sync* endpoints specially here, since the callback state works as a tracker for these requests

numaflow/rust/serving/src/app/jetstream_proxy.rs

Line 111 in 8d8340c

if let Err(e) = notify.await {

The handlers will only send response back to the client when it receives all callbacks.

The confirm_save channel which is used to confirm that the message has been saved successfully to ISB in the previous PR:

• Return success response to client in /async endpoint
• Return early failure message to client /sync* endpoints if saving payload to ISB fails. Else, the handler waits till it receives callbacks from all vertices.