Proposed changes

• Extract "creators" field from indicator and observable objects

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion) - nothing to update - there is no schema documented for Inidicator nor StixObservable objects
• Where necessary I refactored code to improve the overall quality - not necessary within the scope of this ticket

Further comments

If desired, I can add to this PR by extracting the creators field from all objects, not just observables and indicators.