Support dataclasses for queries

Seeing as this client library does not yet support a query builder, I would love to be able to pass in dataclasses when I'm making queries with EdgeQL. It would be something like this:

```py
@dataclass
class QueryStruct:
foo: str = "bar"
... # Ellipsis intended
```

Additionally, if possible, I'd like to see if we could get support for other dependencies such as `attrs` or `pydantic`. Especially with `attrs`, we could support converters and validators to help ensure with the query building process that data is properly being sent.

```py
import edgedb

@attrs.define()
class QueryStruct:
foo: QueryStruct = attrs.field(converter=QueryStruct, validator=edgedb.validate_query_struct)
...
```