[bn] Add language toggle functionality & partial Bengali localization

[debjotyms]

Checklist:

• You have [signed off your commits](https://www.kubeflow.org/docs/about/contributing/#sign-off-your-commits)
• Ensure you follow best practices from our guide. [Contributing](https://github.com/kubeflow/website/blob/master/content/en/docs/about/contributing.md)
• You have included screenshots when changing the website style or adding a new page.

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Description of your changes:

• Updated Bengali localization for the following folders:
  • content/bn/about
  • content/bn/started
  • content/bn/distributions
• Updated the Kubeflow homepage with Bengali localization content.
• Added a language toggle button to switch between English and Bengali versions on the website.

• Ensured all changes are properly signed off.

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Issue:

Fixes: #4092

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Labels:

/area website

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[google-oss-prow]

Hi @debjotyms. Thanks for your PR.

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[debjotyms]

I have copied all the files and folders from the /en to /bn and now localizing one by one. Is that a good approach? If not, then what people usually do in this type of scenarios?

[Arhell]

/ok-to-test