Add spring backend

backend-spring/src/main/resources/application.properties

@@ -0,0 +1,12 @@
+spring.application.name=allowance-planner
+
+spring.datasource.url=jdbc:postgresql://localhost:5432/allowance_planner
+spring.datasource.username=postgres
+spring.datasource.password=postgres
+
+spring.jpa.hibernate.ddl-auto=validate
+spring.jpa.open-in-view=false
+
+spring.flyway.enabled=true
+
+server.port=8080