Rename Tails Installer as Tails Cloner

Now that we are distributing USB images:

• Tails Installer only exists in Tails (it used to be in Debian and Ubuntu as well)
• Tails Installer is no longer the preferred way of installing Tails on USB stick (it used to be the case back in the days)

I think that it’s weird to call it “Tails Installer”. What remains from its use cases is to clone a Tails, either for installing or for upgrading and I think that we should rename it accordingly.

Using the “Use a downloaded Tails ISO image” option of Tails Installer it’s still possible to install Tails without cloning, but as analyzed on #16906, I guess that this feature is not used very frequently.

I also expect that renaming to “Tails Cloner” will make it much easier for users to discover that it is possible to do such thing as cloning Tails; keeping in mind that now that we distribute USB images, people never use Tails Installer to install it from scratch.

So this change is not only aesthetic :)