[frontend] fix bulk search not returning HashedObservable (#6522)

[marieflorescontact]

Proposed changes

• add HashedObservable in searchStixCoreObjectsLinesSearchQuery

Related issues

• issue/6522

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)
• Where necessary I refactored code to improve the overall quality

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...