fast way to fetch logging config for a table

On startup, MongoDB needs to fetch the state of all tables' logging config. It does this by opening a metadata:create cursor on each table. This operation is CPU intensive since it needs to merge multiple configs (from table, column group, and file) into one sorted config string before returning to the caller. We could potentially improve MongoDB startup time by creating a special fast-path way to fetch just the state of logging (e.g. "log=(enabled=true)") for a table without going through the expensive config parsing work. This might involve a special flag to metadata:create cursors, or something more exotic.