Enforce css alpha values as numbers

[antgamdia]

Description of the change

This PR updates the stylelint rules to enforce the usage of numeric alpha (like in the opacity property) values. This change would fix #3653.
Additionally, it extends another config that performs an auto-sort of the CSS properties for the sake of uniformity.

Benefits

The opacity will return back to normal in our built postprocessed css.

Possible drawbacks

N/A

Applicable issues

• fixes Right menu not being displayed #3653

Additional information

I don't know the actual root issue; I mean, the opacity as percentages are widely supported in most browsers (eg in chrome from v78), so I don't see why it wasn't been properly rendered. Maybe it was due to a misconfiguration in our sass compiler?

Anyway, I can confirm it works after having built a custom dashboard image:

[absoludity]

I'm assuming that the .stylelintrc.json is the only change for review here (the rest being generated?)

[antgamdia]

I'm assuming that the .stylelintrc.json is the only change for review here (the rest being generated?

Yes, sure, the rest is autogenerated via yarn lint-css command. Well, there is a simple new package added, which is just new stylelint config, but that's all.