[NOID] Solves CI bug with NEO4J_VERSION variable not being available

[ncordon]

Cherry picked from neo4j/apoc#395

What

Changes System.getProperty("NEO4JVERSION") for project.hasProperty("neo4jVersionOverride") in the docker images version.

Why

Because when they've updated the TeamCity jobs to bump the neo4j version, NEO4JVERSION was never available because it was never set a system property, causing the docker containers to say:

  Caused by: org.testcontainers.containers.ContainerFetchException: Can't get Docker image: RemoteDockerImage(imageName=neo4j:5.8.0-enterprise, imagePullPolicy=DefaultPullPolicy(), imageNameSubstitutor=org.testcontainers.utility.ImageNameSubstitutor$LogWrappedImageNameSubstitutor@278fe428)

Further down the file we do set the neo4j version correctly for the Java artifacts:

ext {
    publicDir =  "${project.rootDir}"
    neo4jVersionEffective = project.hasProperty("neo4jVersionOverride") ? project.getProperty("neo4jVersionOverride") : "5.9.0"
    testContainersVersion = '1.17.6'
}