Add DROP IDENTITY, OVERRIDING SYSTEM VALUE to PostgreSQL clauses (#820)

Quick PR to recognize `DROP IDENTITY` and `OVERRIDING SYSTEM VALUE` as
one-line clauses

Author: nene

src/languages/postgresql/postgresql.formatter.ts

@@ -169,6 +169,7 @@ const tabularOnelineClauses = expandPhrases([
   'DROP FOREIGN TABLE',
   'DROP FUNCTION',
   'DROP GROUP',
+  'DROP IDENTITY',
   'DROP INDEX',
   'DROP LANGUAGE',
   'DROP MATERIALIZED VIEW',
@@ -208,6 +209,7 @@ const tabularOnelineClauses = expandPhrases([
   'LOCK',
   'MOVE',
   'NOTIFY',
+  'OVERRIDING SYSTEM VALUE',
   'PREPARE',
   'PREPARE TRANSACTION',
   'REASSIGN OWNED',