[doc] Improve Pulsar Deployment Kubernetes (#5102)
[doc] Improve Pulsar Deployment Kubernetes (#5102)

### Motivation
Improve the language and the overall descriptive style of the Pulsar Security document (deploy-Kubernetes section): http://pulsar.apache.org/docs/en/next/deploy-kubernetes/

### Modifications
Adjust the tone, personal pronouns, voice also some typo errors of some sentences in the document.
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