VPC/Subnet design for Cells

Overview

In #25067 (closed) we are deciding if we are going to have a multi-project set up or single project setup.

After we do that we need to decide:

• If we use VPC Peering/Shared VPC/Private Connect Service
• Subnet for a single cell or multiple cells

Action Items

• Create an Architecture Decision Record on the decision we end up with.
  • Example of ADR: gitlab-org/gitlab!132129 (merged) / gitlab-org/gitlab!142391 (merged)
• Update Architecture Diagram