Add separate DOJ diagram with S3 and backend systems in an agency bou…

…ndary.

documents/doj-diagram.md

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+# Forms Platform - DOJ architecture diagram
+
+Sample diagram of a potential DOJ deployment of the Forms Platform.
+
+```mermaid
+flowchart LR
+    subgraph "External Users"
+        formFiller[Form Filler: Submits forms]
+        formCreator[Form Creator: Uses no-code interface to create forms]
+        formReviewer[Form Reviewer: Reviews submitted forms]
+    end
+
+    subgraph "DOJ Boundary"
+        subgraph "Agency Systems"
+            direction TB
+            agencyBackend[Agency Backend Systems: Receives submitted form data]
+            s3Bucket[Amazon S3: Stores completed forms]
+        end
+
+        subgraph "Forms Platform (Internal)"
+            webServer[Node.js Web Server: Handles form creation, submission, and interactions]
+            database[(Postgres DB: Stores form data and user information)]
+        end
+    end
+
+    subgraph "External Systems"
+        loginGov[Login.gov: Handles authentication]
+    end
+
+    formCreator -->|Creates forms using| webServer
+    formFiller -->|Submits forms via| webServer
+    formReviewer -->|Reviews submitted forms using| webServer
+    webServer -->|Stores and retrieves form data from| database
+
+    webServer -->|Authenticates form creators via HTTPS| loginGov
+    webServer -->|Submits form data to Agency Backend via HTTPS| agencyBackend
+    webServer -->|Uploads form PDFs to S3 Bucket via HTTPS| s3Bucket
+```