Wire the frontend to Open Match, change /play to POST with latencies

[zmerlynn]

• Changes the /play API to the following structure, vs a single latency:

type PlayRequest struct {
    PingByRegion map[string]int32 `json:"pingByRegion"` // region -> ping time in milliseconds
}

• Changes /play to a POST
• Wires the /play method to the Open Match ticket format from #135. The client uses the watch function (which is better than the polling the fake frontend does), cribbed-ish from: https://github.com/googleforgames/open-match/blob/main/examples/demo/components/clients/clients.go

Tested with the super advanced:

for i in {1..4}; do 
  curl -H "Authorization: Bearer ${TOKEN}" -H "Content-Type: application/json" --data '{"pingByRegion":{"us-central1":50, "europe-west1":100, "asia-east1":150}}' http://35.238.207.159.sslip.io/play &
done

[markmandel]

FYI @kennycoder that we made this change.