Add code suggestions buffer storage
What does this MR do and why?
It adds buffer storage for code suggestions tracking information. It will be moved to CH later on with next MR. The feature is behind a feature flag and does not face users.
MR acceptance checklist
Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.
Related to #441485 (closed)
Edited by Pavel Shutsin