Previous behavior:
Disk images are being accumulated in GCP for a few years, but this
generates unneeded costs as we're not using images older than 1-2 weeks.
Expected behavior:
Delete previously unused images based on a timefrime.
Solution:
Delete images created on a pull request older than 30 days, from the
`main` branch if older than 60 days, and any other image older than 90
days.
A TODO is on place as we'd like to keep at least the 2 latest images of
each type (zebra checkpoint, zebra tip, lwd tip). Once we've excluded
those images, we can delete any older images after 1 week.
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