## Problem
We've started sending slack notifications for failed container image
pushes that are being retried. There are more messages coming in than
expected, so clicking through the link to see what image failed is
happening more often than we hoped.
## Summary of changes
- Make slack notifications clearer, including whether the job succeeded
and what retries have happened.
- Log failures/retries in step more clearly, so that you can easily see
when something fails.
## Problem
We've seen quite a few CI failures related to pushes to docker hub
failing with weird error messages that indicate maybe docker hub is just
not reliable.
## Summary of changes
Retry container image pushing up to 10 times, and send a slack message
if we had to retry, regardless of the job succeeding or not.
## Problem
Release CI is slow, because we're doing unnecessary work, for example
building compute images on storage releases and vice versa.
## Summary of changes
- Extract tag generation into reusable workflow and extend it with
fetching of previous component releases
- Don't build neon images on compute releases and don't build compute
images on proxy and storage releases
- Reuse images from previous releases for tests on branches where we
don't build those images
## Open questions
- We differentiate between `TAG` and `COMPUTE_TAG` in a few places, but
we don't differentiate between storage and proxy releases. Since they
use the same image, this will continue to work, but I'm not sure this is
what we want.
