Include apache license on env file module for antlr generated files

[haidubogdan]

Follow-up of env file support.
It seems to be a relevant thing during development.
All generated antlr parser files should have the license header to not block development while doing license checks run.

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[matthiasblaesing]

This change is good and ensures the license header is in place. If this came up on a rat run, then this is not strictly necessary though. rat should be run on a clean checkout.