Update README to reflect versions that are actually tested against

[mattwillsher]

The README.md Requirements has a section stating which OS's and versions the role is tested against. This is out dated and needed updating against the current GitHub workflows.

A section can be added to point to the vars folder listing files for OS versions for which there is a default configuration.

[Jakuje]

My reading of the README is "this or previous versions were tested on these OSes" (either manually or in CI). We have automation for current OS versions, but we do not have any for the *BSD variants, while we still list them.

[spetrosi]

Information about supported OSes is stored in meta/main.yml via galaxy_tags field https://github.com/willshersystems/ansible-sshd/blob/main/meta/main.yml#L51-L70

[mattwillsher]

I was going to update the wording a bit and remove any OS that are end of life.

[Jakuje]

I do not have issue with either way. What I wanted to point out is that the current is not technically wrong, but removing the EOL ones is totally ok.

Just a note that RHEL6, or CentOS 8 Stream are technically EOL too, while we keep the CI running as some customers might have their support subscription still active and we are still interested in managing them.