It can be confusing to know where to put startup code. We should make a "do startup things after FCV is initiated" function so people know where to put those checks.

We should also look into renaming fassertInitializedAfterStartup since it is misleading and might not apply to replica sets. Replica set members only initialize their FCV version after replSetInitiate has been run. and so fassertInitializedAfterStartup() being called by mongod_main.cpp isn't relevant for them