Polish Tails Installer in Ubuntu PPA

The first iteration (#10407 (closed)) makes Tails Installer available in a Ubuntu PPA, and the web installation assistant (#8580 (closed)) points users to Tails Installer package. Once this is done we can polish whatever needs to be.

Subtasks

#10414 (closed)
#10665 (closed)

Related issues

Blocked by #10407 (closed)

Original created by @intrigeri on 10664 (Redmine)

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