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.