Expose refs and/or prop for scroll event listener

[rebeccaalpert]

We should expose refs for the scrolling message box and/or messages, or a prop for a scrolling event listener so users can use more complex scrolling logic than what we currently supply.

Right now you can't scroll up while using a fixed div with a ref.

This was a request from Red Hat Developer Hub Lightspeed.

[rebeccaalpert]

@karthikjeeyar may have time this quarter and offered to help; otherwise we'll try to fit this in by Q1 at the latest.

[karthikjeeyar]

@rebeccaalpert In RHDH lightspeed, we are still using "@patternfly/virtual-assistant": "2.0.0-alpha.61" where the ref is not available but I checked the latest code, I already see a ref is exposed in chatbot 2.1.0-prerelease.17. I think this is enough for the consumers to handle complex scroll behaviours based on their usecases. we can close this issue, wdyt?

[rebeccaalpert]

That's fine by me! Let me know if you need something else and we'll reopen this.