Add a new dbCheck parameter called validateMode. This parameter will be required when the feature flag is enabled, but should be marked as optional for now.

This parameter determines which consistency checks that dbCheck will run. The three possible values are:

• dataConsistency: Runs the existing data consistency checks between nodes of a replica set. This is intended for cases where running secondary index checks is too expensive, and we want to just test data consistency between nodes in a replica set
• dataConsistencyAndMissingIndexKeysCheck: Runs the existing data consistency checks between nodes of a replica set. Also verifies that there are no missing index keys in all index tables
• extraIndexKeysCheck: Verifies that there are no extra index keys in the index table