Database sample data, make target and go code

backend/internal/database/sample_data/0010_sample_data.sql

@@ -0,0 +1,7 @@
+INSERT OR IGNORE INTO users (username, password) VALUES
+    ('admin', 'password'),
+    ('user', 'password');
+
+INSERT OR IGNORE INTO projects (name, description, owner_user_id) VALUES
+    ('Project 1', 'Description 1', 1),
+    ('Project 2', 'Description 2', 2);