feat: add -T/--timestamps (env LOGPROXY_TIMESTAMPS) option to prepend strftime to each line

[mk-fg]

Might work to address [ ] option to add a timestamp before each log line in the README.
Not sure if it's the best way to do it, but was easy enough to add this way, to address my own use-case.
Feel free to merge with any kind of edits and tweaks, preserving commit/attribution does not matter to me at all.

Thanks for making this small tool.
It's especially useful in modern non-shell invocations with a proper wrapper mode and configuration via env vars.

[CLAassistant]

All committers have signed the CLA.

[thebaptiste]

Many thanks you for your PR.
It works perfectly when the new option -T is used. But without this option, every log line starts with (null) !
It's because, in spawn_logproxy_async, with -T \"%s\", the NULL value for timestamp_prefix is replaced by (null) and passed to log_proxy
Adding this test in log_proxy main fix the problem :
if ( strcmp( timestamp_prefix, "(null)" ) == 0 ) timestamp_prefix = NULL;
I didn't find any better way to fix it, so I will take your PR with this fix.

[mk-fg]

Thanks.

My bad wrt prefix arg, added an option to wrapper as an afterthought and didn't think to test it without prefix.
Other fix can probably be using something like prefix_args = timestamp_prefix ? sprintf("-T \"%s\"", timestamp_prefix) : "" in the wrapper, and templating that into the command line.
And I think it'd be easier if wrapper wasn't using a string command, but an array of arguments, where such stuff can be appended or not as-needed, as also suggested in #37 for a different reason.

[thebaptiste]

I'm not the lead maintener of log_proxy (@thefab is very busy these days) and you're probably a better python developer than me !
So feel free to open any improvement PR.

Meantime I will release 0.6.0 with your new option (which by the way was in our roadmap since several years !)

Thanks again

[mk-fg]

It's C, not python, but yeah sure, I'll make a PR today or tomorrow.

[thebaptiste]

Yes C ! So I will wait for your PR before releasing.

[mk-fg]

Created it as #38, which should address this issue and #37, as described there.