Add node label to etcd metrics

[fungusakafungus]

targetRef on endpoints surfaces as
__meta_kubernetes_endpoint_address_target_kind/__meta_kubernetes_endpoint_address_target_name
in prometheus and gets converted to the label node by
prometheus-operator

What type of PR is this?

/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[etcd] Added node label to etcd metrics

[k8s-ci-robot]

Hi @fungusakafungus. Thanks for your PR.

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[cristicalin]

@fungusakafungus nice cosmetic fix!

/ok-to-test
/lgtm

[floryut]

@fungusakafungus Thank you

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: floryut, fungusakafungus

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