Emit event for auction creation related to an existing campaign

Is your feature request related to a problem? Please describe. Emit an event upon auction creation if this auction is related to a campaign in the campaign module

This solution allows emitting information that can be reused by a backend solution to list auctions of a campaign instead of relying on a non-efficient query

Describe the solution you'd like Create a new event

type CampaignAuctionCreated struct {
  campaignID uint64
  auctionID uint64
  coordinatorAddress string
}

The event is emitted in the hooks logic if the selling coin is a voucher and the auction creator is the coordinator of the campaign

campaignID := getCampaignIDFromVoucher(auction.SellingCoin)
if campaignID
  if auction.auctioneer == getCoordinator(campaignID)
    emit(...)

Describe alternatives you've considered

Create a proposal for fundraising to add campaignID in auction creation message This solution badly reduces the independence and abstraction of the fundraising module. This solution would make more sense if we rename campaign into project and make the campaign module more general purpose. An auction has a projectID and is always linked to a "project" which could be a new chain to launch, a smart contract project, a chain already launched, etc.... This change would imply lot of refactoring for the campaign module and investigation on how to make the module general purpose with a clean design
Create a proxy message for auction creation in campaign that includes the campaign ID Would increase complexity of the campaign module since we should support different auction types. Increase also the complexity of the API

tendermint / spn

Emit event for auction creation related to an existing campaign #823