[Feature]: Consider using schema/appdata event model in core/app

[aaronc]

Summary

We can adopt a more flexible and performant event model by using cosmossdk.io/schema/appdata events in core/app and code which implements that API.

Problem Definition

The event model in core/app simply replicates the key-value Comet/Tendermint event model that we have had for years. While some users may be totally satisfied with this model, many are not as evidenced by ADR 032 which came from representatives three important organizations in the ecosystem.

The major blockers in adopting the resulting typed events more widely were:

• the implementation pushed JSON marshaling into the state machine layer which was a performance layer
• the mapping of protobuf JSON to Comet key-value pairs was a bit awkward (it quotes strings for instance)

We have even heard that some users would like the SDK to manage its own events and not send any events to Comet at all.

Proposed Feature

The event model in cosmossdk.io/schema introduces an alternative which allows:

• either JSON marshaling or mapping of key-value attributes to be produced lazily in a separate go routine (see https://github.com/cosmos/cosmos-sdk/pull/21305), and
• a native JSON event model and storage that would allow users to stop using Comet's events altogether

We could adopt it in core/app and consequently STF and AppManager and then implementors can choose whether they render events as key-value pairs, JSON, or skip rendering events at all depending on their performance and UX needs.

[julienrbrt]

Re-opening as it hasn't been implemented in stf yet.