max_lag is in nr of actions but lag is in nr of bytes

[viktorerlingsson]

Should we maybe rename one or both to make it clearer what it means?

Discussion from here #805 (comment)

maybe max_lag_in_actions / lag_in_bytes?
maybe add lag_in_actions?

---

We go for a simple "lag_in_bytes", for 2.0. good enough.
In future release, we re-construct lag metrics and config so it makes more sense or is clearer for user.