FORCE QUOTE flag can't be specified in flags

Example query that I'd like to generate:

```sql
COPY (
select id
from customers
limit 1
)
TO STDOUT
WITH CSV HEADER QUOTE AS '"'
FORCE QUOTE id;
```

However, due to the logic in `format_flag()` it's not possible to pass `force_quote="id"` or `force_quote=["id"]` or `force_quote=("id",)` when calling `copy_to()` as it calls `repr()` in each case on those values.

I'm happy to create a pull request if this project is still being maintained?

Perhaps a solution could be to whitelist certain flag names and treat them differently when formatting?

Beginne damit, format_flag() und den Einstiegspunkt copy_to() zu lesen, um nachzuverfolgen, wie force_quote-Werte formatiert werden. Bestätige die Änderung, indem du sicherstellst, dass die Formen string, list und tuple das angeforderte FORCE QUOTE id SQL einschließlich der Beispielabfrage erzeugen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.