Plugin defaults do not apply when plugin is not registered

[kurkle]

Plugin defaults do not apply when the plugin is not registered globally.

Originally posted by @simonbrunel in chartjs/chartjs-plugin-datalabels#327 (review)

[stockiNail]

@kurkle apologize because I discovered having a look that issue but I didn't open an issue here. I was thinking that maybe it was working as design.