nsqd: add support for configurable max-defer-timeout for DPUB

[c3llus]

Background

Currently, NSQD does not support a dedicated max-defer-timeout configuration for deferred publish operations. Instead, deferred publish times are implicitly governed by the max-req-timeout configuration. ref

Changes Done

1. new max-defer-timeout command line options
2. default 1h for max-defer-timeout
3. refer to the new max-defer-timeout instead of the old max-req-timeout when doing deferred publish, for:
   a. HTTP
   b. TCP
4. implemented backward compatibility when max-defer-timeout is not explicitly set, it falls back to max-req-timeout

TODO

• update the nsqd docs

[c3llus]

hi @mreiferson, just following up on this PR; would really appreciate your review when you have time!

Thanks!

[mreiferson]

The implementation is fine in general, but a few things:

1. Let's not rename "timeout" to "delay"
2. For users who are currently setting --max-req-timeout and expecting it to effect defers, there's probably some backward compatibility we want to add here. Maybe, if --max-defer-timeout is not set and --max-req-timeout is, we set the defer timeout to the req timeout?

[c3llus]

Thanks for the feedback, @mreiferson! :)

I’ve updated the naming to stick with timeout instead of delay. Also added backward compatibility, when --max-defer-timeout isn’t explicitly set, it falls back to --max-req-timeout like before.

Let me know if there’s anything else you’d like to see adjusted!

[mreiferson]

This is great, thank you! Can you squash down the commits, please?

[c3llus]

pushed the squashed commits. let me know if you'd like any further tweaks, @mreiferson! :)