More verbose logs when running airflow check_migrations (apache#15662)

Currently it just shows "TimeoutError: There are still unapplied migrations after 60 seconds. " which is not that helpful.

This commit adds more info to show the difference in migrations in DB and source code running `check_migrations`:

Now:

```
TimeoutError: There are still unapplied migrations after 60 seconds. Migration Head(s) in DB: {'e165e7455d70'} | Migration Head(s) in Source Code: {'a13f7613ad25'}
```

closes apache#15650

airflow/utils/db.py

@@ -613,7 +613,10 @@ def check_migrations(timeout):
             if source_heads == db_heads:
                 break
             if ticker >= timeout:
-                raise TimeoutError(f"There are still unapplied migrations after {ticker} seconds.")
+                raise TimeoutError(
+                    f"There are still unapplied migrations after {ticker} seconds. "
+                    f"Migration Head(s) in DB: {db_heads} | Migration Head(s) in Source Code: {source_heads}"
+                )
             ticker += 1
             time.sleep(1)
             log.info('Waiting for migrations... %s second(s)', ticker)