Setting version of java_export() jar via command line flag

Is there a way to set the version number of the published jar on the command line? If I use an environment variable in the maven_coordinates, it almost works, but it's not substituted in the pom template. I can create my own pom template and do the string replacement via `--define=` but then I need to set the version in two places. Once by exporting the variable for its use in `maven_coordinates` and again in a `--define=maven_version=0.0.0`. Is there a better way to set the version once on the command line and get it applied to the `maven_coordinates` and the pom file? I've seen a lot of projects using a jenkins build number as part of the published jar version.

```py
java_export(
name = "export",
maven_coordinates = "group:pkg:$MAVEN_VERSION",
)
```

Start by tracing the java_export() entry point and how maven_coordinates and the POM template receive values. Check whether one command-line version can be propagated to both locations, and verify that the published JAR coordinates and generated POM use the same version.

Written by the indexing model from the issue text.