Add a Docker Compose setup with debugging and testing realm (#27)

Configure Keycloak to allow attaching a debugger (localhost:8081).

Add a testing realm with suitable example entries, and explain how to update and export the realm.

Reviewed-on: #27

testing/compose.yaml

@@ -0,0 +1,17 @@
+services:
+  keycloak:
+    image: quay.io/keycloak/keycloak:26.6.0
+    pull_policy: always
+    command: "start-dev --features=declarative-ui --import-realm"
+    environment:
+      KC_BOOTSTRAP_ADMIN_USERNAME: admin
+      KC_BOOTSTRAP_ADMIN_PASSWORD: admin
+      KC_LOG_LEVEL: info
+      KC_DEBUG: true
+      KC_DEBUG_PORT: "*:8081"
+    ports:
+      - "8080:8080"
+      - "8081:8081"
+    volumes:
+      - ./import:/opt/keycloak/data/import/
+      - ../attribute-endpoints-provider/target/attribute-endpoints-provider-1.0-SNAPSHOT.jar:/opt/keycloak/providers/attribute-endpoints-provider.jar