Update K8s cluster metadata

[theletterf]

Updates the K8s cluster monitor metadata to reflect that kubernetes.stateful_set.desired and kubernetes.stateful_set.ready are now default metrics.

[atoulme]

Please run scripts/docs/make-docs to regenerate docs.

[theletterf]

@atoulme I'm stuck. Can't run the script. Could you help?

[jeffreyc-splunk]

@atoulme I'm stuck. Can't run the script. Could you help?

@theletterf I'll try to make the changes and push to your branch.

[jeffreyc-splunk]

@theletterf I'll try to fix the remaining failures in a separate PR and rebase your branch. For future reference, after making changes to metadata.yaml, you can try running:

$ make dev-image
$ make run-dev-image

# you should be in the dev-image container now
$ make signalfx-agent
$ AGENT_BIN=$(pwd)/signalfx-agent make docs
$ exit

Then check and commit/push the locally changed files.