Automatic merge from submit-queue (batch tested with PRs 39855, 41433, 41567, 41887, 41652)
Add fluentd monitoring to fluentd-gcp image
Right now we are not able to monitor the state of fluentd in cluster, which may result in logging subsystem quietly failing. This PR tries to address that problem by introducing the fluentd container monitoring:
* fluentd internal metrics, like number of buffers and number of data in buffers
* `logging_line_count`, number of lines, read by fluentd from application containers' logs
* Has `tag` label, corresponding to the fluentd tag of the entry
* `logging_entry_count`, number of entries, emitted to the output plugin
* With label `component` set to `container`, generated by application containers
* With label `component` set to `system`, generated by system components like kubelet, docker, scheduler, etc.
* Has `tag` label, corresponding to the fluentd tag of the entry
CC @fabxc @igorpeshansky @edsiper
bb5fdff58b