Add a new event for invalidated votes

[kderme]

A new vote can replace an older one if the voter and the action is the same. For tools like DBSync it would be very useful to have a way to mark invalidated votes, using a new event, which can look like
GovReplacedVote (TxId c) [(Voter c, GovActionId c)]

Votes are also removed when dreps are retired and actions are dropped. However these cases are more straight forward for db-sync to handle without events.

Initial requests IntersectMBO/cardano-db-sync#1798

Alternative attemps
db-sync could query its db, to verify that a vote is replaced. However this replicates the logic and forces disk queries for every vote. Using the event queries are necessary only for replacing votes. Using the ledger state without an event would be also hard, since db-sync doesn't have the state before each transaction.