Draft: Resolve NXCALS-6818 Make system optional if specify id

Merge request template

With this change, it will be possible to specify the id of an entity or variable without specifying the system.

DataQuery.builder(spark).variables().idEq(1L).timeWindow("2047-01-01 00:00:00", "2047-01-02 00:00:00").build()

---

@acc-logging-team - please have a look for approval.

Please describe the merge request here.

Closes NXCALS-6818