Set log level to FINEST

[ckreisl]

All log calls in generateChangelog(..) call debug.log(Level.FINEST,...); but not in this case.
This is flooding the Jenkins System Log in case of larger REPO manifest.xml files.

From my point of view everything should be set to Level.FINEST and one can enable a dedicated Log for this particular class.

Testing done

(no tests done just decrease log level)

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