Add Position paramenter for InlineMessage

Just like KMessageWidget, add a position property that defines
whether the message is to be intended in an header are, footer or
inline in the page, as as KMessageWidget does, disable the relevant
borders to make it look more like a toolbar header

The default is Inline, and existing users won't change look at all

![Screenshot_20240221_141914](/uploads/b0aa723b15318d98e4aae3733c47935f/Screenshot_20240221_141914.png)