Add graphical README.md to catalog-server

java-sdk/radar-catalog-server/README.md

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+# Flow
+
+Below are several sequence diagrams illustrating the flow of the application during startup and regular operation.
+
+## Startup
+
+On startup, an init container (kafka-init) will be launched to add configured topics to the Kafka schema registry.
+
+This is done using the [docker/topic_init.sh](../../docker/topic_init.sh) script, which calls the `radar-schemas-tools` 
+command line app
+
+```mermaid
+sequenceDiagram
+    participant kafka-init as kafka-init
+    participant kafka as Kafka
+    participant schema-registry as Schema Registry
+
+    kafka-init ->> kafka: Create topics
+    kafka-init ->> schema-registry: Register schemas
+```
+## Regular operation
+
+After startup the `catalog-server` application will be running and listening for requests on public endpoints. 
+This application is responsible for providing the source-types on requests, which are configured in the [specifications](../../specifications) folder.
+
+```mermaid
+sequenceDiagram
+    participant client as Client
+    participant catalog_server as Catalog Server
+
+    client ->> catalog_server: Request source-types
+    catalog_server ->> catalog_server: Read source-types from /specifications/
+    catalog_server ->> client: Return source-types
+```