[exporterhelper] Add user facing documentation for the batching capabilities

[dmitryax]

Add a configuration section for batching capabilities in https://github.com/open-telemetry/opentelemetry-collector/tree/main/exporter/exporterhelper#configuration

[Annosha]

@dmitryax I'm an Outreachy contributor and looking for good first issues, If I can help with documentation part of this issue please let me know?
Thank you.

[dmitryax]

Hi @Annosha, the batching capabilities are still experimental and under active development. So, it's probably not the right time to document them.

Feel free to look at issues with good first issue label in core and contrib