Make Tails Upgrader suggest a manual upgrade to decrease future IUK sizes

When IUKs get “too big”, link to advanced doc for #15288. Or, if we detect that the upgrade took a long time (1> hour), we can show the link after the IUK was downloade1d (but before IUK installation).

Related issues

Related to #15290
Blocked by #15288

Original created by @anonym on 15289 (Redmine)

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