Document the supported Debian distribution versions

[gbartolini]

As part of the issue raised in #277, we have realised that we have not done a good job defining the supportability of Debian versions. The sudden removal of bullseye from the official Postgres Docker images has forced us to build system images with the new bake system.

We need to add a clear section in the main README file about the distribution versions we support, with dates and links to the official Debian page: https://www.debian.org/releases/

We will guarantee the build of the images for a distribution until the EOL and provide best-effort support to guarantee the build until LTS. Once a distribution is past EOL, we declare it deprecated.

For example:

Name	Version	Release date	EOL	LTS
Trixie	13	2025-08-09	2028-08-09	2030-06-30
Bookworm	12	2023-06-10	2026-06-10	2028-06-30
Bullseye (deprecated)	11	2021-08-14	2024-08-14	2026-08-31

[gbartolini]

I have made a proposal in PR #282

We commit to best-effort support until oldoldstable (bullseye now) reaches LTS date. But if we see that maintainance is too difficult (due to CVEs that cannot be fixed), we can discontinue the build process with a 3-month notice. I think it is fair enough.

[AntonOfTheWoods]

I know this is pretty fresh still but... I was just looking at the image repo and I saw there were images like [17-minimal-trixie](https://github.com/orgs/cloudnative-pg/packages/container/postgresql/504668717?tag=17-minimal-trixie) but also 18-bookworm. It just so happened I wanted to give a 18-minimal-trixie a try but that doesn't exist. I tried to have a look around the actions but couldn't work out whether there was supposed to be a 18-minimal-trixie or not.

I guess maybe this is just an example of the kind of support information that it would be useful to have in the documentation you want to write :-).

[gbartolini]

I guess maybe this is just an example of the kind of support information that it would be useful to have in the documentation you want to write :-).

Rolling tags are part of #284 and #285

[AntonOfTheWoods]

Rolling tags are part of #284 and #285

Thanks. Not sure I completely follow - I guess they are "rolling tags" but none of the examples I put above would seem to be covered by the patterns mentioned in #285. In any case, I eagerly await the documentation :-).