B-77826: fix issue where pom.properties is not copied before war is packaged

The pom.properties, which contains the artifactId and groupId reported by the /buildinfo, needs to be copied to the META-INF directory before the war is packaged. Otherwise, the file will be missed.

This PR bounds the copying of that file to a "prepare-package" Maven lifecycle, which should be before the "package" lifecycle that the maven-war-plugin is bound to.