Add a blueprint for Gitaly Adaptive Concurrency Limit
This MR adds an initial blueprint for Gitaly Adaptive Concurrency Limit.
- Management epic: &10734 (closed)
- Review app for better readability: https://main-ee-122775.docs.gitlab-review.app/ee/architecture/blueprints/gitaly_adaptive_concurrency_limit/index.html
Edited by Quang-Minh Nguyen