Buffer operator

### Discussed in https://github.com/paillave/Etl.Net/discussions/433

<div type='discussions-op-text'>

<sup>Originally posted by **ctrlaltdan** May 16, 2023</sup>
Hi, I was wondering if there is any support for a Buffer operator (specifically mirroring the `Buffer(timeSpan, count)` Rx operator.

Use case is to parse and load chunked output onto a service bus queue.</div>