chore: import upstream snapshot with attribution

examples/official-site/sqlpage/migrations/44_authentication_example.sql

@@ -0,0 +1,18 @@
+create table users (
+    username text primary key,
+    password_hash text not null,
+    role text not null
+);
+
+-- Create example users with trivial passwords for the website's demo
+insert into users (username, password_hash, role)
+values
+  ('admin', '$argon2i$v=19$m=8,t=1,p=1$YWFhYWFhYWE$ROyXNhK0utkzTA', 'admin'), -- password: admin
+  ('user', '$argon2i$v=19$m=8,t=1,p=1$YWFhYWFhYWE$qsrWdjgl96ooYw', 'user'); -- password: user
+-- (the password hashes can be generated using the `sqlpage.hash_password` function)
+
+create table user_sessions (
+    session_token text primary key,
+    username text not null references users(username),
+    created_at timestamp not null default current_timestamp
+);