Add the umbrella section Concepts #2987
Description
New structure mind map: https://miro.com/app/board/uXjVO-EJIyE=/
Plan of the grand restructuring: https://www.notion.so/tarantool/Tarantool-CE-c075d0db9ce24893beca704c145ae501
Product: Tarantool
Audience/target: analysts, product managers
Epic: Restructuring Tarantool docs
SME: @ NeraverinTarantool
Details
This is an epic estimated at 29sp. But it should be done in a single PR. So let's perceive it as a single (but huge) task.
Details and decomposition can be found in the PR: #3116.
Resolving this issue will also resolve #2805