Doc: Adding topics for pg_test_fsync

[JingRan-Yang]

closes: #ISSUE_Number

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Change logs

Describe your change clearly, including what problem is being solved or what document is being added or updated.

Added two new MD files for the documentation of the pg_test_fsync utility, one in English, one in Chinese.
Updated the sidebars.ts file so that the topic can be displayed on the website.

Due to my limited knowledge on postgreSQL, feel free to correct me if wrong.

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[github-actions]

Hiiii, @JingRan-Yang welcome!🎊 Thanks for taking the effort to make our project better! 🙌 Keep making such awesome contributions!

[JingRan-Yang]

@TomShawn Hi Tom, could you help review the topics and see if any adjustment is needed? Thanks!