[Toolkit][Shadcn] Update Button CSS class, remove as props

[ker0x]

Q	A
Bug fix?	yes
New feature?	no
Deprecations?	no
Documentation?	no
Issues	-
License	MIT

This PR update the CSS class of the Button component according to official Shadcn documentation.

It also removes the as props and relies on the presence of an href attribute to determine which element to use.

[Kocal]

Thanks Romain that's super appreciated! I'll take a good look at all of this tonight :)

[Kocal]

Hey, I was finally able to take some time on your contribution, I did few minor changes, but everything is good:

1. I re-introduced the as tag, I prefer to make it explicit and this behavior is closer to asChild from React
2. I modified some examples to reflect the current Shadcn's Button documentation

[Kocal]

Thank you @ker0x.