API: support wal replay status api

[yeya24]

Signed-off-by: Ben Ye ben.ye@bytedance.com

Support the WAL Replay Status API https://prometheus.io/docs/prometheus/latest/querying/api/#wal-replay-stats.

From the document, there should be another field state:

$ curl http://localhost:9090/api/v1/status/walreplay
{
  "status": "success",
  "data": {
    "min": 2,
    "max": 5,
    "current": 40,
    "state": "in progress"
  }
}

But I cannot find it from the prometheus code https://github.com/prometheus/prometheus/blob/main/web/api/v1/api.go#L1375.

[yeya24]

Anyone could help with reviewing this? @beorn7 @kakkoyun Thank you!

[kakkoyun]

LGTM