v3.2 non-config shards and later always return ConfigServerMetadata in command responses, so the ConfigServerMetadata::opTime field should not be boost::optional anymore.

1) Remove the opTime.is_initialized check from ShardingEgressMetadataHook::_advanceConfigOpTimeFromShard():

auto opTime = configMetadata.getOpTime();
if (opTime.is_initialized()) {
    grid.advanceConfigOpTime(opTime.get());
}

2) Make _opTime non-optional in config_server_metadata.h:

    boost::optional<repl::OpTime> getOpTime() const {
        return _opTime;
    }

private:
    boost::optional<repl::OpTime> _opTime;