Execute annotation only supports standard lifecycle phases due to use of enum

The Execute annotation defined at https://github.com/apache/maven-plugin-tools/blob/6dfbd4b6e2674b81702d3417e57b471afad40535/maven-plugin-annotations/src/main/java/org/apache/maven/plugins/annotations/Execute.java#L45 only supports one of the predefined phases from https://github.com/apache/maven-plugin-tools/blob/master/maven-plugin-annotations/src/main/java/org/apache/maven/plugins/annotations/LifecyclePhase.java.

That can't be used for custom lifecycle ids, though.
There should be another element on that annotation which should allow to use custom ids (as regular String values).