Fix sonar warnings after migration to Java 17

After migration to Java 17, Sonar complains that we should `record`s for immutable classes, `Stream.toList()` etc.

See https://sonarcloud.io/project/issues?resolved=false&types=CODE_SMELL&sinceLeakPeriod=true&id=com.exasol%3Aproject-keeper-root for the complete list.