Release Environments - Replace external-dns image from Bitnami

Context

Bitnami have announced that their large repository of open source charts/docker images are now being put behind a paywall effective August 28th, 2025 (https://github.com/bitnami/charts/issues/35164).

To remediate it, in https://gitlab.com/gitlab-com/gl-infra/release-environments/-/merge_requests/407, we changed from using bitnami to bitnamilegacy repository for external-dns. However, it is not a long term solution because:

• Bitnami won't maintain and update bitnamilegacy , so we won't get new versions
• We will be in a passive position if bitnamilegacy is removed in the future

Thus, we should migrate to another external-dns image.

Hints 💡

We have an infrastructure-wide effort in production-engineering#27243 (closed). We should wait until that task is done, and then use the new Helmfile, or implement similarly.