Introduce a new extension point for modules to provide extra content to the geoserver home page, just like
CapabilitiesHomePageLinkProvider does for the getcapabilities panel.
The interface would be pretty much the same:
Except returned components are meant to be part of the main home page
body instead of the right caps panel, and it'd be valid to return null
(so that a provider may choose under what circumstances to return
content at all, like in whether the admin is logged in, etc.)