We want to be able to run dbcheck tests on older versions with the featureFlagSecondaryIndexChecksInDbCheck feature flag turned on for testing (similar to in the all_feature_flags variant). There is no all_feature_flags variant on older versions, so we should create our own custom variant that turns on the featureFlagSecondaryIndexChecksInDbCheck feature flag and runs any suites that are relevant to dbcheck with it.

This ticket is for 5.0.