Add Prehook and Pretimestamp features: this allows "time" key come first

[ikedam]

Multiple log files can be sorted with sort if "time" key comes first. For example:

$ cat node1.log nod2.log node3.log | sort
{"time":"2022-08-06T08:02:01Z","level":"info","node":"node1","message":"foo"}
{"time":"2022-08-06T08:02:12Z","level":"info","node":"node2","message":"bar"}
{"time":"2022-08-06T08:03:03Z","level":"info","node":"node1","message":"bar"}
{"time":"2022-08-06T08:03:10Z","level":"info","node":"node3","message":"bar"}
...

It would be useful in environments where logs aren't managed with log managing systems like Google Cloud Logging, AWS CloudWatch, and so on.

What I did:

• I added Prehook() feature. It calls hooks just before "level" is added to the buffer.
• I added Pretimestamp() feature. It adds timestamp hook with Prehook.

[tfogo]

+1 for this feature. I was just about to ask about adding prehooks and found this PR. Prehooks like this will be useful for making logs more easily human readable.

@rs is there any interest in adding this feature? (Thanks for your work on zerlolog btw, it's great!)

[tfogo]

Hi @rs, sorry to bother you again. I just wanted to check in to see if this is something you would consider adding? If there's anything I could do to help get this merged, please let me know.

Thanks again for all your work on zerolog.

[rs]

I'm not comfortable adding such complexity just for field ordering. I would recommend using tools to read JSON logs instead of dealing with raw output.

[ikedam]

Thanks for comments. Close with won't merge.