Add Documentation link to each Sample

[morning4coffe-dev]

What would you like to be added:

Add a Button with a Documentation link to every Sample. Depending on the control the links could refer to Microsoft, Uno/Theme/Toolkit/... Guidelines and Documentation.

Why is this needed:

Improves the user experience and provides them with more information about specific control.

Note for contributors:

A DocumentationLink is already on every Sample, but it is currently displayed only in the Footer only on Android and iOS. A similar implementation can be applied to make this available on all the platforms.