Restructure spring application properties

Previously, we load three different application-(prod/dev/local).properties with repeating configurations. With this MR, we use spring.config.import to load specific configuration that overwrites the default values.

By default, the application.properties is set to prod configuration, which is why prod.properties is empty. To change the profile, set the SPRING_PROFILE env to either dev or local.

Based on: https://docs.spring.io/spring-boot/reference/features/external-config.html#features.external-config.files.importing