Support Copy function of Postgresql

### Feature Description

Hi team, when i using **cloud-sql-connector-r2dbc-postgresql** as the connector to get DB connection, it Connection type would be **CloudSqlConnection** which not support COPY function of Postgres. In order to use COPY, i can't use gcp:postgresql as protocol and need to add IAM auth during create DB connection
Can we support the COPY function somehow?
Or provide a API to get delegate Connection in **CloudSqlConnection**

### Sample code

```Java
no, but you can try to use COPY when you are using cloudsql as DB driver.
```

### Alternatives Considered

As i know, should don't have, if you guys have some any suggestion or other way, please let me know. Thanks

### Additional Details

cloud-sql-connector-r2dbc-postgres version is 1.28.3
r2dbc-postgresql version is 1.1.0
my DB driver is pool
in order to use COPY function, i updated the DB protocol from gcp:postgresql to postgresql