[Docs] Metric-server deployment

[sachincool]

1. Add supporting docs for metric-server deployment in kops docs
2. this comment Really helped me, I spent a long time searching why my kops nodes gave API-auth fails or even IP missing in SAN's of certificate

[olemarkus]

As of kops 1.19 (currently in beta), metrics server can be installed as an addon by setting spec.metricsServer.enabled: true. The correct flags will then be passed on.

If you want to install through other means, the docs should be added there, I think.

[sachincool]

@olemarkus Great to know! makes things easier. saw #10022 Thanks for your hard work! 🔥 ⭐ 😄