Intent of TestCreateNextActivityTimer_HeartbeatTimer_NoWorkflowExpiry, TestCreateNextActivityTimer_HeartbeatTimer_BeforeWorkflowExpiry

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
    
    TestTimerSequenceSuite/ 2 tests
    
    go.temporal.io/server/service/history/workflow/TestTimerSequenceSuite/TestCreateNextActivityTimer_HeartbeatTimer_BeforeWorkflowExpiry Introduced here
    
    go.temporal.io/server/service/history/workflow/TestTimerSequenceSuite/TestCreateNextActivityTimer_HeartbeatTimer_NoWorkflowExpiry Introduced here