Implement WAR file packaging support

[plaird]

Spring Boot applications are normally packaged as executable jars, but there is also support for packaging them as WAR files.

• https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#howto-create-a-deployable-war-file
• https://docs.spring.io/spring-boot/docs/current/maven-plugin/reference/htmlsingle/#repackage