nsqd: add support for configurable max-defer-delay for Deferred Publish

[c3llus]

TL;DR

Currently, NSQD does not support a dedicated max-defer-delay configuration for deferred publish operations. Instead, deferred publish times are implicitly governed by the --max-req-timeout configuration, which (I believe) was originally intended for requeueing messages? This creates a bit of confusion since requeueing and deferring are two different operations. Ideally, there should be a dedicated setting to control the maximum defer time.

Proposed Changes

Add a new --max-defer-delay config for NSQD, which specifically limits deferred publish times without affecting the requeue timeout. This would make the system more flexible and reduce the confusion between the two operations.

_{Next Steps: If this sounds good, I’d love to help by submitting a PR to implement it. This is one of my first contributions to open source, so I would really appreciate any feedback and help from the maintainers to make sure everything is on track!}