[MNG-7338] Automatically activate batch-mode and make output quiet when running in CI.

[MartinKanters]

After a discussion with @rmannibucau, @slawekjaranowski and @michael-o, I think this is the best solution.
The env CI check is done in Java code, making it easy to unit test. Also, a new flag had to be added to de-activate the CI=true behavior (named --force-interactive). To make it consistent I created an additional flag/alias to -B (--non-interactive). The flags were suggested by @michael-o since it's also used in other widely used CLI tools such as SVN.

Happy to hear your thoughts.

Relevant maven-integration-testing PR

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[MartinKanters]

Thanks for merging master in and the approval @gnodet . I'm on holidays for the next couple of weeks, so feel free to merge it, if you want.