Support replaying past last successful workflow task completion

[bergundy]

Is your feature request related to a problem? Please describe.

Currently in Core based SDKs (and possibly Go and Java) the replayer only replays tasks that have an associated WORKFLOW_TASK_COMPLETED event.

This limitation makes it hard for users to debug workflow task failures using the replayer.

Describe the solution you'd like

Make it possible to "replay" past the last workflow task completion.

Additional context

The value of the isReplaying flag may need to be adjusted and the SDK should not fail replay for commands generated after history ends.