add a config item [security]spilled-file-encryption-method in tidb-configuration-file.md (#4302)
add a config item [security]spilled-file-encryption-method in tidb-configuration-file.md (#4302)

* add a mysql var windowing_use_high_precision

* add spilled-file-encryption-method

* add spilled-file-encryption-method

Co-authored-by: TomShawn <3d0966147538bc5ab020e8dffa2c0b746f9728a6@users.noreply.github.com>
pingcap/docs-cn,pingcap/docs-cn