Redesign plain button padding and hover in design system

[RomijnHumanoids]

During implementation ticket #3446 a new hover for the plain button with indent was suggested. We agreed that this was a better solution than the previous hover state of this specific button with indent.

Now, let's work out what it would mean if all plain buttons use this hover state pattern, if the current padding is needed/desired and what these changes would mean to existing designs that use the plain button. The design system needs to be updated with these changes as well.