Standardised logging timestamp to ISO8601

[tkishore1192]

Atlantis version - atlantis 0.17.0

Issue -
With the current format of logs, the timestamp is printed in the format -
{"level":"info","ts":1623266081.273087,"caller":"server/server.go:715","msg":"All in-progress operations complete, shutting down","json":{}}
This particular format makes it really difficult or impossible to ingest atlantis logs into logging system like ELK. Also to the bare eye it is difficult to understand the format.

Solution offered -
Zap logs can be formatted to be printed in ISO8601 standards. This has been configured in the logger initialisation. With this configs logs are printed in the below format -
{"level":"info","ts":"2021-06-10T00:44:51.559+0530","caller":"server/server.go:148","msg":"Policy Checks are enabled","json":{}}

This format is more readable and easier to ingest into logging system like ELK.

[tkishore1192]

@nishkrishnan - Hello, would it be possible for you to look into this PR? Thank you!

[nishkrishnan]

LGTM

[tkishore1192]

@nishkrishnan - Thanks a ton! Appreciate the quick review. Would you be able to merge this request?

[chenrui333]

Thanks @tkishore1192 for your contribution!