Use the new tails.net domain on the website

⚠ Conditions to merge

• Have @sajolida review this MR
• Have someone from @foundations-team review this MR
• Make sure !1145 (merged) has been released on %Tails_5.14.
• Make sure tails-dev@ and tails-l10n@ are notified about schedule and impacts of this change.

Proposed schedule

Between releases, so there's lower traffic:

• Jun 13: Announce to lists
• Jun 14: Release 5.14
• Jun 27: Merge this
• Jul 21: Release 5.15