Use dsh-plugin-better-sidebar-plugin-office to add Office three-piece preview for better-sidebar

A web plugin maintained by HuanLinOTO, which splits the .docx/.xlsx/.pptx preview from better-sidebar into an independent bundle. Requires better-sidebar >= 0.6.0. Directory command: `dsh plugin add github:HuanLinOTO/dsh-plugin-better-sidebar-plugin-office`; you can also use the npm package `@huanlin/dsh-plugin-better-sidebar-plugin-office`. License: AGPL-3.0.