feat(gpodder): add create_user method to AuthStore

gpodder_sqlite/src/models/user.rs

@@ -14,9 +14,9 @@ pub struct User {
 #[derive(Insertable)]
 #[diesel(table_name = users)]
 #[diesel(check_for_backend(diesel::sqlite::Sqlite))]
-pub struct NewUser {
-    pub username: String,
-    pub password_hash: String,
+pub struct NewUser<'a> {
+    pub username: &'a str,
+    pub password_hash: &'a str,
 }
 
 // impl NewUser {