customize logger format

Is this a BUG REPORT or FEATURE REQUEST?: feature request

What happened: collect kubeless container log to elasticsearch

What you expected to happen: specify logger format to fulfill customized log filtering pattern

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version): 1.17
• Kubeless version (use kubeless version): v1.0.8
• Cloud provider or physical cluster: AWS EKS