docs(etw): add SessionName parameter to service-etw configuration table

[Copilot]

SessionName was added to EtwInput in this PR but omitted from the plugin documentation, leaving users unable to discover or correctly configure the feature.

Changes

• docs/cn/plugins/input/extended/service-etw.md: Added SessionName row to the configuration parameters table, documenting its type (string), default value (empty string = system-assigned name), and the stop-and-recreate behavior triggered when a session with the same name already exists at startup.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[Takuka0311]

百炼自动化审查：建议保持开启。

本 PR 为已合并的功能 PR #2580 补充缺失的 SessionName 参数中文文档。变更仅涉及单行文档更新，内容与代码实现一致，属于有效的文档完善工作。当前处于 Draft 状态，需维护者审查后合并。.

最佳落地路径：

保持开启。建议作者或维护者将本 PR 标记为 Ready for Review，核对文档格式与 #2580 实现细节一致后合并，以完善 service-etw 插件用户文档。.

已核对内容：

• pr_diff: 本 PR 在配置参数表格中新增 SessionName 行，说明类型、默认值及同名 session 处理行为。. 公开文档：docs/cn/plugins/input/extended/service-etw.md。 (docs/cn/plugins/input/extended/service-etw.md:51, 760ffd45112a)
• merged_feature_pr: PR fix(input_etw): harden ETW session cleanup and naming #2580 已合并，实现了 SessionName 参数逻辑，但未同步更新文档。. (plugins/input/input_etw/etw_input.go, f034aa1c0fd1)

百炼审查备注：模型 qwen3.6-max-preview；对照提交 768cf9d283dc。