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
The characteristics of a list are
o the order of the entries is significant
o duplicates are allowed
The characteristics of a set are
o the order is not significant
o duplicates are not allowed.
When describing keys for a step the characteristics of a
set applies here, whereas the characteristics of a list does
not apply.
