showDateTime needs dateTimeFormat too

What does this MR do?

The CI template for java maven builds already contains the parameter -Dorg.slf4j.simpleLogger.showDateTime in order to include timestamps in the maven logs. But this parameter alone doesn't lead to the desired result. As the maven documentation states, the number of milliseconds since start up will be printed, if the format is not specified or is invalid. So therefor I added this missing format.

Does this MR meet the acceptance criteria?

Conformity

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