Intent of ignores_a_zero-valued_target_time

All 2 exact tests in this concept. Every test is marked by where it enters the hierarchy.

go.temporal.io/ 2 tests
- server/ 2 tests
  - service/ 2 tests
    
    history/ 2 tests
    
    workflow/ 2 tests
    
    TestTimeSkippingTransition/ 2 tests
    
    fast-forward_fallback_and_gating/ 1 test
    
    go.temporal.io/server/service/history/workflow/TestTimeSkippingTransition/fast-forward_fallback_and_gating/ignores_a_zero-valued_target_time Introduced here
    
    go.temporal.io/server/service/history/workflow/TestTimeSkippingTransition/nil_safe Inherited nil_safe