feat(fluent-bit): set system-node-critical as a default priorityClass

[m00lecule]

Issues:
#54

In Kubernetes there is a good practice to specify a system-node-critical priority class for monitoring agents running as daemonsets.

ref: https://kubernetes.io/docs/tasks/administer-cluster/guaranteed-scheduling-critical-addon-pods/

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[m00lecule]

@lisguo may I ask for a review?

[m00lecule]

@lisguo May I ask for a review again? The Integration tests are failing due to Error: Credentials could not be loaded, please check your action inputs: Could not load credentials from any providers which doesn't seem to be connected with my changes.