docs: app uml with example

Signed-off-by: Arsen Gumin <gumin@live.ru>

proposals/000-rest-submit-server/new_app.puml

@@ -0,0 +1,12 @@
+@startuml
+actor User
+participant "REST Submit Server" as REST
+participant "Kubernetes API" as K8s
+participant "Spark Operator" as Operator
+
+User -> REST: POST /sparkapplications (CRD as JSON)
+REST -> K8s: CreateNamespacedCustomObject (go-client)
+K8s <--> Operator: Existed behaivor
+K8s --> REST: Event/Status
+REST --> User: Response (200 OK / Details)
+@enduml

proposals/000-rest-submit-server/proposal.md

@@ -41,6 +41,8 @@ Deploy a companion HTTP server with the Spark Operator that:
 5. **Supports TLS termination** via mounted certificates (cert-manager or manual).
 6. **Emits** structured logs and exposes Prometheus metrics for request counts and latencies.
 
+7. ![Create spark app exmaple](./spark_app_post_uml.svg)
+
 ### User Stories (Optional)
 
 #### Story 1