Add a section on Connection flows

Closes gitlab-org/build/team-tasks#28

See merge request gitlab-org/gitlab-ee!3562

Geo - Does not sync repos on unhealthy shards in non-backfill conditions

Closes #3690

See merge request gitlab-org/gitlab-ee!3540

As part of the architecture, say what ports are used by what services
when.  This should add value in debugging data flows, and opening
firewalls.

Fix wiki retry count typo

Closes #4177

See merge request gitlab-org/gitlab-ee!3569

[EE] Hashed Storage Attachments migration path

See merge request gitlab-org/gitlab-ee!3544

[EE] Strip leading & trailing whitespaces in CI/CD secret variable keys, and environment scope

Closes gitlab-ce#40561

See merge request gitlab-org/gitlab-ee!3563

Add new API endpoint - get a namespace by ID

See merge request gitlab-org/gitlab-ee!3450

[EE] Refactor the way we pass `old associations` to issuable's update services

See merge request gitlab-org/gitlab-ee!3537