Combobox: document UI pattern design-wise

[davicostalf]

Summary

We currently have a primitive componente called Combobox that makes it easier to implement components related to this interaction. However, there are no design resources to guide a Combobox interaction. Since this pattern is hard to encapsulate in an all-encompassing component, maybe we should start by documenting some guidelines and offering Figma resources. We should also summarize everything we have experimented so far (and we have experimented a lot 😅).

Rationale

No response

[felipepowlist]

There's this exploration we did a while back @davicostalf

[davicostalf]

Related with discussion #553