Make sure we get alerts above certain levels of disk usage in our instances

[ioannakok]

Background

We recently found ourselves in a position where DCR instances were very close to using all their disk space (~99.4%). This PR reduced the artefact to less than 40% of its original size.

Task

This ticket is to make sure we set up a CloudWatch alarm for exceeding certain levels of disk usage in our instances (not just DCR instances). Possibly 80%?

[VDuczekW]

what do we need to do: set up alert

[rhiannareechaye]

Reopening (closed by mistake)

[ioannakok]

PR that further reduces the size of the artefact: #7499