Merge branch 'docs/cell-communication' into 'master'

Update FAQ about cell communication

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/149406



Merged-by: Kamil Trzciński <ayufan@ayufan.eu>
Approved-by: Kamil Trzciński <ayufan@ayufan.eu>
Co-authored-by: Steve Xuereb <sxuereb@gitlab.com>

doc/architecture/blueprints/cells/index.md

@@ -319,8 +319,7 @@ For example, users on GitLab Dedicated don't have to have a different and unique
 
 ### Can different Cells communicate with each other?
 
-Up until iteration 3, Cells communicate with each other only via a shared database that contains common data.
-In iteration 4 we are going to evaluate the option of Cells calling each other via API to provide more isolation and reliability.
+Not directly, our goal is to keep them isolated and only communicate using global services.
 
 ### How are Cells provisioned?