[Improvement] Capitalize the title of the document sidebar

The specification of the title of the document sidebar needs to be consistent，It is better to organize a specification
文档侧边栏的标题规范需要保持统一，最好可以整理一个侧边栏标题规范，放到官网规范文档中 https://linkis.apache.org/zh-CN/community/how-to-contribute-to-website/#3-%E8%A7%84%E8%8C%83


Start with the website contribution guidelines at the linked section and inspect the document sidebar titles shown in the issue image. Define the capitalization convention, apply it consistently to the relevant sidebar titles, and add the convention to the website standards documentation.

Written by the indexing model from the issue text.