Implement `Connection::get_option*()`

Related: #7

```rust
pub enum OptionConnection {
/// Whether autocommit is enabled.
AutoCommit,
/// Whether the current connection should be restricted to being read-only.
ReadOnly,
/// The catalog used by the connection.
/// # Since
/// ADBC API revision 1.1.0
CurrentCatalog,
/// The database schema used by the connection.
/// # Since
/// ADBC API revision 1.1.0
CurrentSchema,
/// The isolation level of the connection. See [IsolationLevel].
IsolationLevel,
/// Driver-specific key.
Other(String),
}
```

Also blocked on https://github.com/ClickHouse/clickhouse-rs/issues/358