Change password in Persistent Storage settings

In https://gitlab.tails.boum.org/tails/blueprints/-/wikis/Persistent-Storage-redesign, I'm adding a Change Passphrase button at the botton of the list of features:

Another "GNOME way" would be to put the Delete and Change Passphrase buttons in the hamburger menu.

Hamburger menus have poor discoverability and 2 out of 3 test participants didn't find the Delete button when I put it there, though admittedly it might be even harder to discover on paper prototypes.

Change Passphrase being for now the only other such button, it doesn't hurt to put it at the bottom of the scroll and will be more discoverable than in an hamburger menu.