Investigate non-file based distrubuted eventing mechanism

[mathewc]

Currently in Functions we leverage the fact that we have a shared file system as an eventing mechanism. For example, our "debug mode" relies on a file watcher on the debug_sentinel file watch mechanism.

In cases where we don't have a shared file system (e.g. Azure Functions on Mesh) we lack this capability. We need to investigate alternatives, and put these features behind interfaces so the implementation can be swapped out (we already do this to a degree).

Ideas include EventGrid, Azure Storage blob/polling, Redis Cache, etc.

[ankitkumarr]

I will move this to the Backlog, as this needs further discussion.