Add extra sample date mapping to oracle sample allow list files

Oracle DATE is a date/time therefore it is expected to be mapped to PostgreSQL `timestamp` or BigQuery `datetime`.

We should add the following extra sample mappings.

samples/allow_list/oracle_to_bigquery.yaml

```
# Oracle DATE is a date/time and valid in DATETIME.
"date": "timestamp"
"!date": "!timestamp"
```

samples/allow_list/oracle_to_postgres.yaml

```
# Oracle DATE is a date/time and valid in TIMESTAMP WITHOUT TIME ZONE.
"date": "timestamp"
"!date": "!timestamp"
```