[bn] Add Bengali translation for kubectl (concepts)

[perashanid]

This PR adds Bengali translation for kubectl (concepts).

Changes Made:

• Translated the page to Bengali

Related Issue:
Part of Bengali localization effort. Split from previous PRs as requested by maintainers to have one PR per translated page.

Checklist:

• Translation follows Kubernetes style guidelines
• All links and references are updated for Bengali locale
• Front matter is properly configured

[k8s-ci-robot]

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