The QGB orchestrator should be able to listen for Valset events

[rach-id]

The QGB orchestrator should be able to listen for Valset events emitted by Celestia-app. This would help it sign the correct valsets and be up to date with the changing valsets. The MVP will need this in order to be complete.

[rach-id]

Also, we need to check if the orchestrator has already signed a valset so that it won't resign it again.
Currently, we're getting the events via:

tendermintRPC.Subscribe(ctx, "valset-changes", fmt.Sprintf("%s.%s='%s'", types.EventTypeValsetRequest, sdk.AttributeKeyModule, types.ModuleName))

and sometimes, we receive multiple events for the same nonce.