Use structured logs (`log.InfoS(...)`)

[antgamdia]

As per the discussion in #4180 (comment)
and #3848 (comment), it would be nice if we moved to structured logs (more info here).

Specifically, it means:

• Use log.InfoS(...) in our log traces.
• Add a --logging-format to our deployments to let users customize the format; for instance, using json-

[castelblanque]

This would be great!
WIth this in place, getting the structured logs indexed in e.g. Kibana would be a no-brainer 😄

[kristinjeanna]

Hi,

I'm interested in working on this. Couple of questions:

1. Is the intent that all go source files in the repo will require this change (i.e., wherever klog is used, switch the logging to structured)? Are some sources out-of-scope for this change?
2. Do you wish this change to follow the same approach as that documented at the k8s page Structured Logging migration instructions?