Fixing 6088 : Download CSV data

[louis49]

Motivation for features / changes

Fixes #6088: Download CSV data

Technical description of changes

Setting good parameters to constructor and adding a default value for an optional parameter

Detailed steps to verify changes work correctly (as executed by you)

Download with no error

Googlers, see b/307370637. @yatbear tested internally at cl/598969320.

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[yatbear]

Thanks for the change! After you resolve the comment, please make sure to acquire the CLA following https://github.com/tensorflow/tensorboard/pull/6719/checks?check_run_id=20415071608.

[yatbear]

Please fix the lint error: https://github.com/tensorflow/tensorboard/actions/runs/7553563538/job/20577640944?pr=6719
You can run black command to auto-format Python files: https://github.com/tensorflow/tensorboard/blob/master/DEVELOPMENT.md#how-to-develop-tensorboard.

[yatbear]

Nice work!

[louis49]

Thank you ! My first merge in a Google product 😀