Implement CI/CD for pilot doc project on VK Cloud docs engine

[p7nov]

We have a pilot docs project on the VK Cloud docs engine: https://github.com/tarantool/doc-md.
As a next step, we need a CI/CD for this project like we have for existing Tarantool docs:

1. Automatic staging of PRs to master. The staging must update on new commits pushed to the source branch.
2. Manual staging deployment of any branch.
3. Production deployment:

• on merging to master
• on schedule (once a day?)
• manual

Note:

• it's a general description. We'll decide on the new docs portal URL and some other details later together with DevX team.
• ожидается помощь/консультации от команды разработки и девопс движка