chore: Change log ts format to RFC3339

[mumoshu]

The TimeEncoder for zap seems to have been set to EpochTimeEncoder which is the default and it was not very readable. Changing it to a TimeEncoderOfLayout(time.RFC3339) for readability.
Another benefit of doing this is the ts format is now consistent with various timestamps ARC put into pod and other custom resource annotations.

BEFORE:

{"level":"debug","ts":1646530339.3554308,"logger":"actions-runner-controller.horizontalrunnerautoscaler","msg":"Calculated desired replicas of 10","horizontalrunnerautoscaler":"default/org-runnerdeploy","suggested":2,"reserved":20,"min":2,"cached":2,"max":10}

AFTER:

{"level":"debug","ts":"2022-03-08T01:30:46Z","logger":"actions-runner-controller.horizontalrunnerautoscaler","msg":"Calculated desired replicas of 2","horizontalrunnerautoscaler":"default/enterprisegroup-runnerdeploy","suggested":2,"reserved":0,"min":2,"max":10,"cached":2}