Add numeric and character types to OpenAPI spec (#1259)

* Add numeric and character types

* Remove decimal type mapping

It is treated as numeric by PostgreSQL so the mapping was redundant.

test/fixtures/privileges.sql

@@ -100,6 +100,7 @@ GRANT ALL ON TABLE
     , "Server Today"
     , pgrst_reserved_chars
     , authors_w_entities
+    , openapi_types
 TO postgrest_test_anonymous;
 
 GRANT INSERT ON TABLE insertonly TO postgrest_test_anonymous;