fix: Add ATTACH, DETACH to PostgreSQL keywords.

Examples of valid, not so rare statements in postgres dialect.

```
ALTER TABLE atable DETACH PARTITION atable_p00;
ALTER INDEX atable_acolumn_idx ATTACH PARTITION atable_p01_acolumn_idx;
```

They fall into same class as `EXTENSION` added in below PR, so let's add them as well.

In the same rationale as #785

Author: filiprem-clickup

sqlparse/keywords.py

@@ -839,6 +839,8 @@
     'CONFLICT': tokens.Keyword,
     'WINDOW': tokens.Keyword,
     'PARTITION': tokens.Keyword,
+    'ATTACH': tokens.Keyword,
+    'DETACH': tokens.Keyword,
     'OVER': tokens.Keyword,
     'PERFORM': tokens.Keyword,
     'NOTICE': tokens.Keyword,