feat: add Brainpool signing algorithms

Add brainpoolP256r1, brainpoolP384r1 and brainpoolP512r1 as available signing algorithms for key generation.

data/ui/managementdialog.blp

@@ -157,7 +157,7 @@ template $LockManagementDialog : Adw.Dialog {
                                             subtitle: C_("Signing algorithm of the new keypair", "Key");
 
                                             model: Gtk.StringList {
-                                                strings: ["ed25519", "dsa3072", "rsa2048", "rsa4096"];
+                                                strings: ["ed25519", "dsa3072", "rsa2048", "rsa4096", "brainpoolP256r1", "brainpoolP384r1", "brainpoolP512r1"];
                                             };
                                         }