feat: add trigger to onZoom context

[kurkle]

Add trigger property to the onZoom context object, indication what triggeder the zoom. Possible values: 'api', 'drag', 'wheel', 'pinch'.

[github-actions]

Size Change: +89 B (+0.43%)

Total Size: 20.8 kB

Filename	Size	Change
dist/chartjs-plugin-zoom.esm.js	7.54 kB	+30 B (+0.4%)
dist/chartjs-plugin-zoom.js	7.68 kB	+29 B (+0.38%)
dist/chartjs-plugin-zoom.min.js	5.61 kB	+30 B (+0.54%)

_{compressed-size-action}

[yubiuser]

Thanks.