Introduce properties to manage enterprise and community fork years

Enterprise code was forked as of 3.4.0-rc02 which was released in 2018. The community code was forked with latest commits in 2020. The 3.4 is outside of Neo4j, Inc. support and therefore no more commits are expected in 2021. Regardless, it will be easier to manage CMI if the years for these forks are handled separately.