Improve position utilities

[alizedebray]

Our current position utility classes allow defining the inset of an element. The classes available are:

• top-[position]
• bottom-[position]
• start-[position]
• end-[position]

where [position] can be 0, 50, or 100.

These classes are generated by the utility API: https://github.com/swisspost/design-system/blob/main/packages/styles/src/utilities/_variables.scss#L448

They are documented here: https://next.design-system.post.ch/?path=/docs/803a58e8-c734-4ad7-80a8-62da1bb29d4b--docs

Goal

Improve these position utilities and their documentation by:

• Using inline/block properties: replace top, bottom, right, and left with
  inset-block-start, inset-block-end, inset-inline-start, and inset-inline-end
• Adding a control for the bottom-* and end-* classes in the position utility documentation