Extend onZoom and onPan callbacks for syncing multiple charts

### Feature Proposal

I have created a PR that extends the onZoom and onPan callbacks with the amount zoomed/panned.
https://github.com/chartjs/chartjs-plugin-zoom/pull/933

This should help everyone trying to sync zoom and pan accross charts. :)

If you could take a look, I'd much appreciate it.

Start by reviewing pull request #933, which contains the proposed onZoom and onPan callback extension. Check that the callback data supports syncing multiple charts as described; the work is done when the proposal is reviewed and accepted by the maintainers.

Written by the indexing model from the issue text.