Docs: Use consistent icon for product tier badges

Product badges are used to indicate that a feature is only available in certain tiers. The product badge is shown when hovering over an icon.

There are two different icons used in the documentation. The sidepanel uses fa-info-circle, but in the text a fa-question-circle-o is used.

This is inconsistent.

The use of fa-question-circle-o has (anecdotally) resulted in confusion. The question mark was interpreted as a link to a help text, explaining the usage or functionality of the feature. Users therefore didn't hover/click the icon and missed that the feature was only available in higher tiers.

This MR standardizes on fa-info-circle.