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
This approach works also in case we are in a subdirectory of the git repo,
e.g. in the closure of a dir statement.
The decission is delegate to git rather than using internal knowledge
about git file names. Well, the directory will be always named '.git',
but nevertheless ...
May endup in a false positive in case we did not clone a repo AND there
is another git repo somewhere upwards in the file system. Maybe some
other git repo is located upstairs containing e.g. the jenkins setup.
The advantage of working also for subdirectories outweights the disadvantage
for the false positive. It is not likely that we have to deal with another
git repo upstairs, since the pipeline script is expected to be located in
the payload git repo. A phantom repo upstairs looks like a pure academical
discussion.
* Make commit of new version optional in `artifactSetVersion` step
You might not want to add a new commit for each version, when versions
are automatically created. This commit makes this feature optional, but
enabled by default to maintain API compatibility.
* Set `gitCommitId` if null
* Improve documentation of `commitVersion` parameter
* Allow to operate in a code checkout without `.git` directory
