Move the helm changelog compilation before the version bump

We also add the new changelog before that

This is previously where the changelog manager was running, moving it to be after the version bump caused issues where we failed to swap to the stable branch again after the changelog compilation, and we were also tagging the changelog commit, which included ci-skip. So release piplelines were not working

Fixes: https://gitlab.com/charts/gitlab/issues/772 Fixes: https://gitlab.com/charts/gitlab/issues/773