Update the CustomersDot architecture diagram
We should update https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/main/doc/architecture/customersdot_architecture.png and the thread model for CustomersDot - this is a follow-up from https://gitlab.com/gitlab-com/gl-security/appsec/threat-models/-/merge_requests/25#note_1307593595
Right now the architecture diagram does not reflect the updated services very well. We should also try to follow other similar diagrams we may have in GitLab to make it a bit more standard