Update the ESA CCI Surface Elevation Change layers

[trey-stafford]

Description

This PR updates the "Glaciology/Surface elevation change" layers to the latest version
(v3) of the Climate Change Initiative (CCI) Surface Elevation Change dataset
from the European Space Agency (ESA). This extends the timeseries to include a
surface elevation change layer for 2016-2020.

Checklist

If an item on this list is done or not needed, simply check it with [x].

• Config lockfile updated (inv config.export > qgreenland/config/cfg-lock.json)
• Version bumped if needed (bumpversion (major|minor|patch|prerelease|build)
• CHANGELOG.md updated
• Documentation updated if needed
• New unit tests if needed

[trey-stafford]

Replaced by decompress_step helper.

[MattF-NSIDC]

I was able to download this by creating a session in the browser and copying my session ID cookie into a wget request:

wget --header="Cookie: sessionid=mysessionsid" "http://products.esa-icesheets-cci.org/products/download/cci_sec_2021.zip"

But I think session IDs are not persistent long-term. The value doesn't work if one character is changed. I think we can probably figure out a way to get a session ID at download time if we want to.