Intent of HeartbeatTimeout_capped_by_StartToClose

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
  - chasm/ 2 tests
    
    lib/ 2 tests
    
    activity/ 2 tests
    
    TestModifiedActivityTimeouts/ 2 tests
    
    go.temporal.io/server/chasm/lib/activity/TestModifiedActivityTimeouts/HeartbeatTimeout_capped_by_StartToClose Introduced here
    
    go.temporal.io/server/chasm/lib/activity/TestModifiedActivityTimeouts/ScheduleToClose_and_StartToClose_set_-_StartToClose_capped_by_ScheduleToClose Inherited ScheduleToClose_and_StartToClose_set_-_StartToClose_capped_by_ScheduleToClose