infrastructure/ops#871 having a month-old version should be a notice

Created by: agh1

This responds to the concerns in infrastructure/ops#871 where people are getting system check warnings because they're on 5.8.x, which is only a month old.

It's good that versions that are only a few months old, with no intervening security releases, are labeled deprecated rather than eol. That makes the language less scary. However, the severity of the system check was still warning. That leaves no room for escalation when the version truly is too old.

Also, it really isn't that any worse to be on 5.8.2 than on 5.9.0, when 5.9.1 is the latest. We know that 5.9.1 fixes bugs, but it may be fixing bugs introduced in 5.9.0, so someone on 5.8.2 could be just fine. The only consideration is that the person on 5.8.2 is one month closer to end-of-life.

This change de-escalates the severity of a deprecated version to notice, and it modifies the status message to explain what it means to be on an older version.