Replace "Debian Live user" with a more descriptive full user name

When locking the screen, the full name of the amnesia user appears: “Debian Live user”. We could have something nicer. Maybe “amnesia”, maybe “Tails”.

But does this have to reuse the same name as the one we would choose for #5655, for anonymity reasons? or can we use something specific for Tails?

Parent Task: #5878 (closed)

Related issues

Related to #5655

Original created by @sajolida on 11256 (Redmine)

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