dex: inventorize useful ABCI events to index

[erwanor]

As part of #3504, we ported all of our event recording to use the ProtoEvent interface. We should run through a few indexing use cases (e.g. an explorer, a price monitoring tool, an event-based trading bot etc.) to check if the ABCI event coverage of the DEX is complete.

[conorsch]

Nice to have for 65 (#3554), but really we can ship without it, and follow up with a point release. The downside of shipping without it is that anyone who wants this functionality would need to reset their node and resync in order to have the older events indexed. We accept that as a downside if it helps us ship 65 sooner.

[zbuc]

Explorer Events

• Position created
• Position reserves changed
• Position closed
• Position withdrawn
• Position reward claimed
• Swap
• Swap Claim
• Batch swap executed
• Arbitrage execution

Price Monitoring Events

• Many of the above events are also useful
• Best priced position changes

Event based trading bot

• Nothing different comes to mind for me here apart from what is already outlined

[hdevalence]

Position reserves changed

Rather than framing this as "position reserves changed", i think it would be useful to frame it as a "position execution", since that's what causes the position reserves to change. That way we can emit events on all the micro-executions as well as for the overall batch execution.

[zbuc]

Going through the code right now and checking off completed events:

• Position created
• Position executed against
• Position closed
• Position withdrawn
• Position reward claimed skipped for now and a comment added since reward claims are unimplemented
• Swap
• Swap Claim
• Batch swap executed
• Arbitrage execution
• Best priced position changes skipping this because implementation is tricky and indexers could implement this based on existing position events.

[zbuc]

Noticed this comment on dex::event::position_close:

    // TODO: should we have another event triggered by the position manager for when
    // the position is actually closed?

I'm not sure what the distinction of "actually closed" here is, but I haven't gone through the call chain yet. Leaving this comment to remind myself.