Cleanup gradle.properties since spotless is fixed for java 17

[sebastian-peter]

There is a known bug in spotless (described here diffplug/spotless#834) which prevents out of the box support for spotless. Therefore we make use of the workaround described here (https://github.com/diffplug/spotless/tree/main/plugin-gradle#google-java-format).

As soon as the issue with spotless is resolved, we should cleanup the gradle.properties again.

(this is a blatant copy of ie3-institute/PowerSystemUtils#200 )