After-commit block action

[mhofman]

What is the Problem Being Solved?

In order to measure the impact of #5934, we need to understand the impact of commiting more data to the IAVL tree. Currently all our telemetry flows through the JS side, using slog events generated by cosmic-swingset and swingset.

In order to get insight into the go side of things, we need to generate an event after go has fully committed its state.

Description of the Design

After commiting, go could send a non-blocking AFTER_COMMIT action. It may be acceptable for this action to re-use the existing BLockingSend mechanism if the JS side doesn't perform overly expensive work during that action.

Consensus considerations

The basic plumbing may actually be a change that has no change on consensus, and may provide valuable telemetry insight outside of state-sync.

Test Plan

TBD

[mhofman]

Taking this on as part of state-sync