MongoDB 4.2 ability to specify FCV 4.0 before first startup

There are some circumstances where the newer MongoDB 4.2 FCV 4.2 Ops Manager backups may not be desired by the customer.

When deploying a new MongoDB 4.2.x instance the data files are created by default using FCV 4.2.

Currently the best and cleanest way to run MongoDB 4.2.x FCV 4.0 data files when deploying a new instance is:

• start MongoDB 4.0.x
• allow it to generate the data files
• finally upgrade it to MongoDB 4.2.x.

It would be nice to have a way to configure MongoDB to create FCV 4.0 data files at startup.