TLAPS Safety Proof of MongoRaftReconfig

Supplementary materials for formal verification of safety of the MongoRaftReconfig protocol in TLAPS, the TLA+ proof system. Includes a formal inductive invariant and a TLAPS proof of the LeaderCompleteness and StateMachineSafety properties. MongoRaftReconfig is a logless dynamic reconfiguration protocol originally designed for MongoDB, a distributed database that uses a log-based replication protocol derived from Raft.