Expose `RecordMetadata` after `send`

I have a use-case in which a fluvio producer needs to keep track of the offsets (and partitions) that it sent its messages to. To that end, I would like to expose the RecordMetadata struct to the python client.

If I understand correctly, the TopicProducer.send method (in rust) generates a ProduceOutput struct, which provides a wait method in the end yielding the desired RecordMetadata.

I see two general ways forward to expose such functionality in the python client:

Introduce both a ProduceOutput and a RecordMetadata to the python world, effectively mirroring the rust variants. This has a weird caveat, though: The ProduceOutput.wait method consumes self, inhibiting any further use of the ProduceOutput object. If a ProduceOutput would also live in the python world, such a "consumption" is not possible to have (if I understand PyO3 correctly). This could be worked around by wrapping the "inner" rust-version of the ProduceOutput in a Cell
```
#[pyclass]
pub struct ProduceOutput {
inner: Cell<NativeProduceOutput>,
}
```
and then using take in the corresponding wait method:
```
#[pymethods]
impl ProduceOutput {
fn wait(&self) -> Result<RecordMetadata, FluvioError> {
    let inner = self.inner.take();
    Ok(run_block_on(inner.wait()).map_err(error_to_py_err)?)
}
*
```
Another option would be to not expose ProduceOutput and directly provide some method send_and_wait_for_metadata (a proper name would need to be found) that calls wait on the result itself and then returns a RecordMetadata object.

Do you have a good idea, how to address this issue?

I would be willing to add a PR for either of the approaches (or another one, if you have an idea).

infinyon / fluvio-client-python

Expose `RecordMetadata` after `send` #389