PM-2290 has two components:

1. Allow config servers to have the shard role
2. Ensure the config and shard roles don't conflict when run together

All existing tests for dedicated config servers test 1) when feature flags are enabled, but getting broad coverage for 2) requires adding new tests, passthroughs, etc., so to buy more time for this, we'll add a second feature flag that prevents running transitionToCatalogShard and transitionToDedicatedConfigServer. That way we can enable the main feature flag guarding 1) in 7.0 and enable the new feature flag when we've finished the test plan for catalog shard mode.