[FEATURE] `interactions` option

[kurkle]

In my opinion hover and tooltips options {mode, axis, intersect} are tightly bound together.
There could be a use case where that is not true, but by default these could be configured using one set of options.

Current Behavior

hover and tooltips options are configured separately. Controllers usually set default for hover.mode, but not for tooltips.mode => weird effects.

Expected Behavior

hover and tooltips options extend from new interactions option.

Possible Solution

• Add interactions option that both hover and tooltips extend from.
• Move defaults (global and chart type specific) to the new option.
• Extend on chart initialization to keep compatibility with external code?

2nd Possible Solution

• Update controllers to set defaults for both tooltips and hover

Context

This would ease the configuration of new charts a bit. Also new developers would avoid weird interaction effects when familiarizing with this library for the first time.

Environment

• Chart.js version: 2.7.3

[benmccann]

Originally discussed in #5857 (comment)