Support K8s-style health check endpoints for Cube Store nodes

**Is your feature request related to a problem? Please describe.**
Cube supports [K8s-style health check endpoints](https://cube.dev/docs/deployment/production-checklist#set-up-health-checks) while Cube Store nodes don't. Hence, it's not easy to understand if the Cube Store cluster and individual nodes have initialized and started properly.

**Describe the solution you'd like**
Provide and document the same set of endpoints for Cube Store.

**Describe alternatives you've considered**
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**Additional context**
Relevant discussion in Slack: https://cube-js.slack.com/archives/C0206EXEVAS/p1621326447001400?thread_ts=1621322103.000300&cid=C0206EXEVAS