Upgrade Postgres Major Version

[rc9000]

TL;DR: do not just merge this right now :)

I did some digging how to navigate an upgrade of the Postgres version, as 13 will be out of support next year. Unfortunately this is a bit of a support headache, since it needs manual converting of the Postgres files. I tried to include an easy one-command approach using the pgautoupgrade project: https://github.com/pgautoupgrade/docker-pgautoupgrade

How to use it is in the README_UPGRADE.md, which the PG 17 container also just dumps into the container log if there is a mismatch.

However most users probably start the container in the background, in Docker Desktop etc. and will still not immediately see it. So we should find a good time to create a new release in Netdisco proper, declare this the cutoff for netdisco-docker PG13, and then I'd hang out in the issues & IRC for a week or two, because people will probably need help :)

To try the instructions or just test Netdisco with PG17 in general, you can get the new container from my Dockerhub account - just use rc9000/netdisco:latest-pg17 as a drop-in replacement for netdisco:latest-postgresql.

Actual EOL for PG13 is November 13, 2025 so there is no rush.

[rc9000]

IRC log: after some discussions we decided that a separate container with pg17 would be nice, that the user can enable at will instead of being forced into it:

14:01 < rc9000> one way i could see instead: we make an alternative netdisco-postgresql17 
                container that includes the autoupgrade but is commented out in docker-compose, plus some notes that the user can
                switch to it when they know they have a valid backup or don't care, or just want to start over with a new db?
14:01 < rc9000> this would be nontrivial since we need to merge the whole pgautoupgrade into our entrypoint, but definitely doable.
14:01 < rc9000> (the relevant bits are around here https://github.com/pgautoupgrade/docker-pgautoupgrade/blob/main/postgres-docker-entrypoint.sh#L567)
15:01 < oliver> rc9000: yes I was thinking along these lines ... a straightforward thing the user could do (change a text config and restart) to opt in to the upgrade
17:10 < rc9000> oliver: ok let's rescope the pr so there is a new container that can be enabled, and then we can slowly get people into switching over.
17:11 < rc9000> that's also nice because there is no big bang
17:14 < rc9000> should we just append the major version like so?
17:14 < rc9000> netdisco:2.084002-postgresql17
17:14 < rc9000> netdisco:latest-postgresql17
17:14 < rc9000> ... time passes
17:14 < rc9000> netdisco:2.084002-postgresql22
17:14 < rc9000> netdisco:latest-postgresql22
17:15 < rc9000> and we could also push the current one additionally as netdisco:latest-postgresql13 for symmetry
17:52 < oliver> rc9000: yes would be OK but I'd like to check for anything like a loop over the suffix on the image name which would be caught out 
                (like for i in do backend frontend postgresql...)