Send estimated wait time when joining a queue

The server already logs the wait time of each search party. This data would need to be aggregated for rating brackets and sent to the client, which can then display it to the user.
Challenges:
- The wait times vary a lot depending on how many people are online, so we would need to factor that in somehow
- we need to come up with a fallback if a particular rating bracket has too little data available

Implementation idea:
We log the wait time together with total online players at that moment and the rating of the matched players. With some linear regressions we can then provide an estimate for a given rating and current number of online players