Etcd v3.3.0 added the --listen-metrics-urls flag which allows specifying
addition URLs to the already present /health and /metrics endpoints.
While /health and /metrics are enabled for URLS defined with
--listen-client-urls (v3+ ?) they do require HTTPS.
Replace the present etcdctl based liveness probe with a standard HTTP
GET v1.Probe that connects to http://127.0.0.1:2381/health.
These endpoints are not reachable from the outside and only available
for localhost connections.
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