Add `dummy_kernels` table for testing `sql_json_merge`

[jopemachine]

Motivation  

• This work is necessary to provide replacement test codes for those removed as breaking changes in PR feat(BA-20): Replace sessions, kernels's status_history's type dict with list #3201.

  Objective  

• Replace obsolete test codes

  Impact  

• Since this task only involves adding test code, it should not affect any services.