out_stackdriver: add k8s_cluster resource type

[ryanohnemus]

Add k8s_cluster resource type to out_stackdriver plugin.

This can be used in combination with the in_kubernetes_events to write k8s_cluster type events to stackdriver (such as any non-Pod based kubernetes events)

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Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change

[INPUT]
    Name kubernetes_events
    Tag k8s_events

[FILTER]
    Name rewrite_tag
    Match k8s_events
    Rule $involvedObject['Kind'] Pod k8s_events.$metadata['namespace'].k8s_pod false
    Rule $metadata['namespace'] .* k8s_events.$metadata['namespace'].k8s_cluster false

[OUTPUT]
    Name stackdriver
    Match k8s_events*k8s_cluster
    resource k8s_cluster
    k8s_cluster_name my-cluster-name
    k8s_cluster_location us-central1

• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature
  out_stackdriver: add k8s_cluster resource type fluent-bit-docs#1284

Backporting

• Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[ryanohnemus]

test failure looks like a flake

[braydonk]

The change looks good to me!

Would you mind adding a test for this as well? You can use this other resource test as a reference. I can intuitively see that this will work based on the implementation, so it's just a matter of getting a test for it.

I'll be good to merge it after a test is added!

[ryanohnemus]

@braydonk, just rebased and pushed with a test. I will watch the CI checks for any failures, but otherwise we should be good to go

[braydonk]

LGTM, unless something in CI fails I will merge.