ADD chromatic for automatic storybook ui diffs

[shajz]

thanks @bsabardu-lucca

[Supamiu]

@shajz more details on this would be nice to have, or close if you consider this as done/outdated.

[shajz]

The idea was to replace the current UI diff system in PRs (which requires a connection to the internal Lucca VPN) by setting up https://www.chromatic.com/ (which doesn't)

@bsabardu-lucca did this with on some Timmi apps (but he's on the PM side of things now), maybe @lfaldalucca can explain a bit more if it's still relevant / still useful