Use links instead of buttons on samples index and descriptions pages

[nikoeno]

I suppose to use links instead of buttons on samples index page and sample description page

Why?
To provide native web links experience.

For example
Links opening in new tab with ctrl+click or mousewheel click
User have a link preview in the browser(usually in bottom-left corner)

[ericwindmill]

Sorry, @nikoeno, we're currently in the process of removing the Samples Index in favor of an index on flutter.dev

I do appreciate the contribution though