Force render on knob button click and update example

[Keraito]

Issue: As discussed on Slack, the callback of the button knob didn't seem to do something. What actually happened was that clicking the button didn't trigger a re-render, so the results of the callback were never visually visible.

There was an example in the official-storybook, but that basically used the knob button inside a react component defined in the stories file and triggered a setState call to force a render of the component itself. The example itself described that this was not the best way to do this.

What I did

1. Force a re-render on button click.
2. Change the example to make the knob button change the values of the injected props to the component.

cc @ndelangen as he was part of the discussion

[codecov]

Codecov Report

Merging #3650 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #3650   +/-   ##
======================================
  Coverage    40.1%   40.1%           
======================================
  Files         479     479           
  Lines        5236    5236           
  Branches      862     862           
======================================
  Hits         2100    2100           
  Misses       2618    2618           
  Partials      518     518

Impacted Files	Coverage Δ
addons/knobs/src/registerKnobs.js	0% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 62e42f8...3a513fa. Read the comment docs.

[Hypnosphi]

Feel free to merge after CI passes

[Hypnosphi]

Please update storyshots: yarn test --core --update

[pvinis]

this doesnt seem to work for react native..