[Feature Request] Opt-in worker support for getting task boundaries in activation

[cretz]

Describe the solution you'd like

For a new use case (user task tracking for purposes of charging on serverless), they want to opt-in to knowing the task boundaries. Make some worker option that, if enabled, sends a StartTask job on the first activation of a task and a EndTask job on the last activation of a task (sending a whole new activation if needed). Ideally the EndTask job has a failure if there is a task failure (would usually infer this from a failure lang sends, but there are core-level failures too).

Note, this is subject to discussion. Maybe we don't want this or something else? I have not opened a feature issue up for task tracking because I am unsure whether this is a pattern we want to perpetuate.