What is the purpose of the change

Add the SQL reference documentation for Seata-go AT mode, including both English and Chinese versions, to help developers understand the supported SQL syntax, functions, and limitations in Seata-go.

Brief changelog

• Add sql-seata-go.md to versioned_docs/version-v2.6/user/sqlreference/ (English version).
• Add sql-seata-go.md to i18n/zh-cn/docusaurus-plugin-content-docs/version-v2.6/user/sqlreference/ (Chinese version).
• Update versioned_sidebars/version-v2.6-sidebars.json to register the new document in the sidebar menu.

Follow this checklist to help us incorporate your contribution quickly and easily:

• Make sure there is a GITHUB_issue filed for the change(usually before you start working on it). Trivial changes such as typos do not necessitate a GITHUB issue. Your pull request should solely focus on addressing this specific issue without incorporating any other modifications. Each PR should resolve a single issue.
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• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Test your code locally by running npm run build, and make sure it works as expected.
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