On withdraw rewards event, there's no value for delegator address

[freak12techno]

Summary

When claiming rewards, the events emitted does not have a field for a delegator address:

cosmos-sdk/x/distribution/keeper/delegation.go

Line 204 in bf85bfb

ctx.EventManager().EmitEvent(

Problem Definition

I am building a tool to track transactions matching the required filters: https://github.com/QuokkaStake/cosmos-transactions-bot.
I am mostly using it to track transactions related to my validator, and one of the use cases for me is tracking the transactions where I claim rewards for my own validator's self stake. I can track transactions for the filter like the following: withdraw_rewards.validator = "xxxx", but that will give me all transactions where someone claimed rewards from my validator, which is not something like I need.

Proposal

I propose to add a "delegator" field to the event emitted, so we can write filters like the following: withdraw_rewards.validator = "xxx" AND withdraw_rewards.delegator = "yyy". This should be backwards compatible while adding more flexibility in how one can write queries.

I can also implement that if needed, as I want to get involved with cosmos-sdk development itself.

[freak12techno]

Appreciate that a lot, especially given how fast this was resolved. Way to go!