Support for Delayed Secondaries in CSRS

MongoDB supports delayed secondaries for general purpose replica sets. In MongoDB 3.2 it is possible to deploy multiple config servers in a replica set configuration, however it is not possible to define a delayed secondary in this configuration.

It would be useful to allow a delayed member in the config server replica set (slaveDelay) to facilitate a sharded cluster being rolled back in time and/or to avoid 'human error' when modifying the data in a config server.