Disable download logs in Maven by default
This commit adds a flag to Maven by default, which disables the messages
like "Downloading from central".
The logger is set to level "warn", so errors will still be visible, but
successful messages won't clutter logs anymore.
This option is also set by default in the GitLab CI template file for
maven.
See [1] for reference on the option.
1: https://stackoverflow.com/a/35653426/8843830