Docs for SERVER-37833: Make DBClient and NetworkInterface retry with multiple keys for internal auth

Description

Description:

This change implements a new cluster keyfile rollover procedure (see the design doc).

Engineering Ticket Description:

This will make the internal clients in the server retry authentication with multiple keys from the keyFile so that mongod's and mongos's that are in the middle of rolling over their keyfiles can continue to authenticate with each other.

Scope of changes

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)