Plan future Weblate upgrades

The Weblate upgrade to a new major version (3 → 4) using the new container-based setup went smooth.

We now need to evaluate the desired frequency of upgrades.

Note that:

• 4.10 is already out.
• minor versions generally can't be skipped, so when we lag behind we accumulate work on upgrading to intermediate verisons.
• from 4.9 to 4.10, the upstream Weblate container image changed it's base from debian:bullseye-20211115-slim to python:3.10.1-slim-bullseye, and such changes might have some impact in the setup for running our custom scripts.