RFC3339Nano timestamps and flags to configure level & format

[croomes]

Sets timestamps to use RFC3339Nano format, and adds command-line flags to configure log level and format.

Currently the -zap-stacktrace-level is hardcoded to panic to avoid stacktraces in the logs for errors that we recover from. kubernetes-sigs/controller-runtime#1348 addresses this.

Previous log entry:

{"level":"info","ts":1611140462.7687058,"logger":"controller-runtime.metrics","msg":"metrics server is starting to listen","addr":":8080"}

New default:

{"level":"info","timestamp":"2021-01-20T15:47:44.042084444Z,"logger":"controller-runtime.metrics","msg":"metrics server is starting to listen","addr":":8080"}

[darkowlzz]

LGTM!