maxStalenessSeconds support for mgo.ReadPreference

[wpjunior]

"Replica set members can lag behind the primary due to network congestion, low disk throughput, long-running operations, etc. The read preference maxStalenessSeconds option lets you specify a maximum replication lag, or “staleness”, for reads from secondaries. When a secondary’s estimated staleness exceeds maxStalenessSeconds, the client stops using it for read operations."

https://docs.mongodb.com/manual/core/read-preference/#maxstalenessseconds