[doc test] test all the docs in kusionstack.io thoroughly, keep docs up to date

[amyXia1994]

docs need to be tested

• [the most important] step by step tutorials must be fluent, without any blocking error, and can be reproduced precisely as documented
• links within the website must be valid
• command line usage doc must be consistent with the actual output
• the terminologies and statements of the same concept must be consistent throughout the website

ways to accomplish the goal

• provide documentation testing scripts and integrate them into CI progress, to ensure that all the update about tutorials won't break the validity of the doc.
• reuse the testing scripts mentioned above to produce demo video & gif
• ref: istio page test:
  • https://github.com/istio/istio.io/blob/master/README.md#testing-document-content
  • https://github.com/istio/istio.io/blob/master/tests/README.md