Automatic merge from submit-queue (batch tested with PRs 60465, 61773, 61371, 61146). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Enable partial success in fluentd-gcp

Enable partial success in fluentd-gcp. This will allow to reduce amount of lost data in case of invalid (e.g. too big) entries: instead of dropping the whole request, only failed entries will be dropped.

```release-note
[fluentd-gcp addon] Partial success option is enabled in fluentd.
```

/assign @x13n 
/cc @bmoyles0117