Rework the release process

[smortex]

Now that we use some of the Vox Pupuli tooling, we want to update the way
we prepare a release: the release:prepare rake tasks from Vox Pupuli
is not unsable with our current setup, so update he prep_version rake
tasks to update the version in both the .ddl and the .json files, and
also write some boilerplate in the CHANGELOG.md file. The call
sequence is the same as used before to release a module:

$ bundle exec rake prep_version VERSION=5.5.0

When the changes are ready, a release is done from the main branch of
the repository by tagging the code and pushing the tag to GitHub where a
GitHub action will do the actual release:

$ git tag 5.5.0
$ git push --tags

[smortex]

To test these changes with modulesync:

$ bundle exec msync update --noop

(A diff of each change is shown, the files in modules/... are updated and can be inspected)

These changes can also be reviewed from the PR directly: the Run msync --noop against all modules test has a Run msync --noop tasks that basically run this command direct link.

Without --noop, modulesync will commit the changes in each repo and push the branch to GitHub. Providing a custom commit message can be great:

$ bundle exec msync update --message "Rework the release process"

I like to use the gh command to open Pull-Requests when the changes are ready, I usually go with:

$ bundle exec msync execute -- gh pr create --fill --draft