ci: check the sidebar of document site

[seeflood]

What would you like to be added:
CI should check the sidebar of document site.
The rule might be: "All the document under docs/zh and docs/en should be added into the sidebar"
For example:

• All document under the docs/zh/start and docs/en/start directory should be added into the sidebar
  

• All doc under the docs/zh/blog directory should be added into the sidebar
  An example is doc: layotto rpc code analysis #494 (review)
  

Why is this needed: