Allow reporting of weathermap items (or image items)

[nbz6]

Feature Request

Is your feature request related to a problem? Please describe

The reporting doesn't allow to add a weathermap as an item of the reporting.

Describe the solution you'd like

Add a hook to allow plugins to add new items, like a weathermap item.

But it will still be necessary to develop the specific code in the plugin weathermap.

Describe alternatives you've considered

Add an item "Image" to allow to add a local image from a custom URL.
This could be used to add a custom logo in the report, but also weathermap from link like :
/cacti/custom_logo.png
/cacti/plugins/weathermap/weathermap-cacti-plugin.php?action=viewimage&id=zzzzzzzzzzzzz

Additional context