release_process: consider adding --img to the idf-content call

Spotted while preparing the 3.12 release, the following call in release_process.mdwn:

./bin/idf-content \
   --version "${VERSION:?}" \
   --iso "${ISO_PATH:?}" \
   > "${RELEASE_CHECKOUT:?}"/wiki/src/install/v2/Tails/amd64/stable/latest.json && \
cat > "${RELEASE_CHECKOUT:?}"/wiki/src/install/v1/Tails/amd64/stable/latest.yml <<EOF
[…]

After discussion with anonym (who looked at the image verification code, if I got this right), we decided to add a --img option for the latest.json file.

We should probably decide whether to revert that (amending the latest.json file); or to keep it and amend the documentation.

(There’s also latest.yml which wasn’t modified, but I suppose this was for v1 and need to stay the same, while v2 lets us have several images?)

Original created by @CyrilBrulebois on 16396 (Redmine)