Rework deb/rpm package build

Description

Use Rocky Linux to build rpms for RHEL 8 and 9

Rocky is the new CentOS.
Build deb for each distribution

We've had issues with debian builds in the past, because we had the expectation that building on one version of debian would produce a shared lib which will execute on other debian-derivatives. Differences in glibc versions make this impossible (see https://github.com/timescale/promscale_extension/commit/68a1dab760cc0845659b8242f50595e1d23d6ba9).

The above exposed differences in lintian, and an issue in the way that it was being invoked. The simplest fix is to disable erroring on warnings, which reduces the number of lints that we need to ignore.
Add information about when each distribution will be EOL

I keep on forgetting, so having a link to the details helps.
Rework release-tester make target

This is a slightly experimental approach. There is an inherent mismatch between make's file-oriented approach, and docker's "image stored in daemon" approach. The intermediate steps have been reworked to produce a file artifact, which should prevent having to rebuild things all of the time.

This change prompted the removal of .deb and .rpm from .dockerignore as those files are required to build the release-tester make target.

Please take into account the following non-code changes that you may need to make with your PR: