Human-readable timestamp

[masa213f]

What

Some k8s operators developed by Neco outputs the unix time stamp.
It hard to read for us. Let's use Human-readable timestamp format.

{"level":"info","ts":1657611644.746192,"logger":"runner","msg":"Runner listener exit with retryable error, re-launch runner in 10 seconds.","pod":"neco-apps-runner-6b95fc5688-8x95n"}

How

Set time encoder. Refer to the following:
https://github.com/cybozu-go/nyamber/blob/db1370fcb6443fdfb0f95f7061749db041a35cf2/cmd/nyamber-controller/main.go#L66
https://github.com/cybozu-go/nyamber/blob/db1370fcb6443fdfb0f95f7061749db041a35cf2/controllers/suite_test.go#L68-L70

Checklist

• Finish implementation of the issue
• Test all functions
• Have enough logs to trace activities
• Notify developers of necessary actions