Add more distributions in the test matrix

[evelikov]

Currently we have a bunch, although a few more won't go amiss. Namely - Fedora (see #396), RHEL, CentOS Stream (see #350) and Suse (opensuse (see #399) or SLES).

It's likely we don't need all of these, I'm listing them since they're explicitly mentioned across the codebase.

[anbe42]

please drop Debian 9 from the test matrix, it has been recently archived

[evelikov]

please drop Debian 9 from the test matrix, it has been recently archived

Done with #331.

I wonder how is ELTS supposed to work, given that one cannot get the packages even?

[anbe42]

The archived releases are still available from http://archive.debian.org/ ... but at some point you need to tell apt to ignore the expired signatures done with expired keys ...

ELTS is managed on Freexian (not Debian) infrastructure: https://www.freexian.com/lts/extended/docs/how-to-use-extended-lts/

[evelikov]

With #399 - we've got a pretty decent variety of distributions and variations in our CI.

While there are no enterprise-y distros like RHEL or SLES, I suspect we can close this :-P