This is an important metric to keep track of and be aware (maybe even
alert on) when consumers fall behind consuming stream messages. While
they should be able to catch up, if they fall behind too much and the
stream gets truncated, they may miss on messages.
This is something that we want to expose via Prometheus metrics as well,
but we've started closer to the core, CLI & Management.
This should be merged as soon as it passes CI, we shouldn't wait on the
Prometheus changes - they can come later.
Pair: @kjnilsson
Signed-off-by: Gerhard Lazu <gerhard@lazu.co.uk>