[Core] Task Event Buffer improvements when using event aggregator pathway

[sampan-s-nayak]

Description

• ensure that the task event buffer buffers events until the dashboard agent (which houses the event aggregator) is up and running.
• today if tasks are run before the dashboard agent is up, tasks events will be lost (if the task event buffer -> event aggregator pathway feature flag is turned on)

once this issue is fixed, we will also need to update all tests marked with a todo linking to this issue