Add the ability for "Events" to happen at a specific point on a Path

[jasondaming]

This is tied to this PathWeaver request: wpilibsuite/PathWeaver#245

There was discussion on discord about doing this via time or position and it seemed decided that position is ideal and time is easy.

This isn't high priority as teams can currently break up their paths and run events between them.

[Starlight220]

How do we want this to be API-wise? Callbacks for each hook? Something else?

[jasondaming]

I don't currently have a good roadmap for this. I haven't even targeted the event stuff for 2021 in PathWeaver (it isn't super hard but don't want to overpromise). I just created this issue to track it and also help track demand for these features.