Support fluentd as a logging sink

[MattiasGees]

Is this a BUG REPORT or FEATURE REQUEST?:

Uncomment only one, leave it on its own line:

/kind bug
/kind feature

What happened:
Our Fluentbit implementation at this moment only support Elasticsearch as a logging sink. This limits where you can log to. A lot of people want to use other logging tools (cloudwatch, logz.io, ...) and they are not able to use these tools together with our logging solution.

What you expected to happen:
Have more freedom in how you can configure the logging sink

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

Anything else we need to know?:
Fluentbit is limited in logging sinks, maybe it would be a good idea to extend fluentbit to use fluentd as output? This way we let the user configure their own fluentd setup and give them a lot of freedom.

This maybe would also solve #474.

Environment:

• Kubernetes version (use kubectl version):
• Cloud provider or hardware configuration**:
• Install tools:
• Others: