Have Tails Upgrader automatically point to manual upgrade if running from an old version

Originally created by @sajolida on #12493 (Redmine)

See #12392 (closed).

“Old” here means “definitely too old to have an IUK”. We are currently publishing IUKs for 2 versions so version older than 12 weeks will never have IUKs.

Note that we might decide to publish more IUKs in the future. So it would be good to have a mechanism in place to remember updating this setting if we decide to ship more IUKs.

This mechanism would also become obsolete if we decide to do #11131 (comment 57704).

Related issues

• Related to #12492 (closed)
• Related to #14544 (closed)
• Related to #15288 (closed)