[FEATURE] Improve the process of publishing doc changes to documentation repo

[dai-chen]

Is your feature request related to a problem?
Currently, there are 2 places for both SQL/PPL documentation: doc/ folder in SQL repo and https://github.com/opensearch-project/documentation-website. Before every release, we have to post another PR in doc repo manually like this: opensearch-project/documentation-website#830

What solution would you like?
One possible solution is to embed our RST doc to documentation website. Then we can get tech writer review it in each PR with doc changes. For new doc, they can review it when we post PR with embedded link to doc repo. This may lead to webpage style or other problem, however, we should start thinking about how to improve this anyway.

What alternatives have you considered?
Automate the process to convert RST doc to markdown and send PR to doc repo with little manual work. But this still requires to maintain two copies of documentation. Any comment on the PR in doc repo has to be merged back to our repo. Unless we can get tech writer involved in each our PR for early review.

Do you have any additional context?
N/A