Migrate off Bitnami images before Aug 28 (memcached/postgresql/rabbitmq/redis)

[arnxxau]

Bitnami announced that on August 28, 2025 they’re moving most public images to a read-only Bitnami Legacy repo (no updates) and keeping only a small, hardened latest-only set free. That means our Bitnami-based Helm deps will stop receiving security patches and could break on redeploys if tags disappear. We should replace Bitnami images in this chart with well-maintained alternatives.

Current Bitnami charts in use:

• memcached oci://registry-1.docker.io/bitnamicharts - version 7.4.16
• postgresql oci://registry-1.docker.io/bitnamicharts - version 15.5.32
• rabbitmq oci://registry-1.docker.io/bitnamicharts - version 14.7.0
• redis oci://registry-1.docker.io/bitnamicharts - version 20.1.4

Official announcement for context:

• GitHub: Upcoming changes to the Bitnami catalog (effective August 28th, 2025) bitnami/containers#83267
• Broadcom/Bitnami news post: https://news.broadcom.com/app-dev/broadcom-introduces-bitnami-secure-images-for-production-ready-containerized-applications

[ariep]

I've been keeping a fork of this repo for a while in order to add a couple of minor chart features. In this fork I've replaced the bitnami charts deps by ones from groundhog2k. It's not as extensive a collection as Bitnami's, but carries three of the four deps Zulip needs -- memcached is missing but would be relatively easy to add I think. It uses vanilla upstream docker images, not custom ones like Bitnami. It's relatively obscure and not backed by a big company, which is a disadvantage but can also be an advantage like we've now seen with Bitnami. It seems high-quality, consistent among charts, and frequently updated.

If the maintainers think that this is a good choice, I can help create a PR to make this switch.