Only call entrypoint once

[seiferma]

This PR fixes an issue when calling mvn from within the container multiple times or when calling mvn via a command.

The issue occurred because we called the entrypoint from within the mvn command. However, the entrypoint unsets a variable, which is important to run the command in the entrypoint.

In the pull request, the entrypoint is no longer called from the mvn command. Instead, an initialization script is called before running the original mvn binary. In addition, the initialization script only runs once.