chore(db): add flyway migration tool (#48)

Reviewed-on: #48

src/main/resources/application.properties

@@ -10,10 +10,13 @@ spring.datasource.url=${POSTGRES_URL}
 spring.datasource.username=${POSTGRES_USER}
 spring.datasource.password=${POSTGRES_PASSWORD}
 spring.datasource.driver-class-name=org.postgresql.Driver
-spring.jpa.hibernate.ddl-auto=update
+spring.jpa.hibernate.ddl-auto=validate
 spring.jpa.show-sql=false
-spring.sql.init.mode=always
-spring.sql.init.schema-locations=classpath:db/schema.sql
+
+spring.flyway.enabled=true
+spring.flyway.locations=classpath:db/migrations
+spring.flyway.baseline-on-migrate=true
+spring.flyway.baseline-version=1
 
 ## Security
 spring.security.oauth2.client.registration.google.client-id=${GOOGLE_CLIENT_ID}