Fix login button in Header slim

[zetareticoli]

Does a discussion already exist on the topic you are interested in, or on a similar topic?

• I verified and it doesn't exist

What

The Header/Desktop/Full and Header/Mobile/Full variants provide a login button version not available in the BS Italia framework.

The right version is instead available in the variants:

• Header/Desktop/Slim
• Header/Mobile/Slim

Why

It is necessary to bring order in the versions, eliminating those not planned.

Context

No response

More

For the logged user scenario, please consider what adopted for Modello Comuni:
https://italia.github.io/design-comuni-pagine-statiche/servizi/graduatoria-messaggio.html

[zetareticoli]

Never mind, the "Slim header with full responsive button" variant reproduces the one present in the UI kit with the same name.

I'll use this issue to align colors between UI Kit and BS Italia.