feat: add user selection flow

backend/src/main/resources/application.properties

@@ -0,0 +1,7 @@
+spring.datasource.url=jdbc:h2:file:./data/hemhub;MODE=PostgreSQL;DATABASE_TO_LOWER=TRUE;DEFAULT_NULL_ORDERING=HIGH
+spring.datasource.username=sa
+spring.datasource.password=
+spring.jpa.hibernate.ddl-auto=validate
+spring.jpa.open-in-view=false
+spring.flyway.enabled=true
+