chore(nsqd): added documentation for max-defer-timeout

[c3llus]

Background

Previously, NSQD's deferred publish timeout was implicitly governed by the max-req-timeout configuration. With the introduction of a dedicated max-defer-timeout option in NSQD, the documentation needs to reflect this new behavior and configuration.

Changes Done

1. added documentation for the new max-defer-timeout command line option, including its default value and fallback behavior.
2. updated the /pub and /mpub HTTP API documentation to clarify that the defer parameter is now governed by max-defer-timeout.
3. added a section explaining the deferred publish timeout and its backward compatibility with max-req-timeout.

Related PR

• NSQ PR #1504

TODO

• merge after corresponding NSQD release

[mreiferson]

Thanks!