As part of PM-1970, we changed the default read concern to be local. The behavior before this was for reads targeting primaries to have local read concern behavior but reads targeting secondaries have available read concern behavior. However, we didn't provide a way for users to return to these semantics if they wanted to, since manually setting read concern available (or within cluster wide read concern) also affects read concern for primaries.

We should add a way to let users opt into the previous behavior.