Add stats block for meeting attendees

Is your feature request related to a problem? Please describe.
As an admin I input a number of participant when I close my meeting. This can be considered as an important stat to be shown on the homepage and the participatory space presentation page.

Describe the solution you'd like

Add a stats block to show the number of attendees in the participatory space presentation page in the activity section and on the homepage block “Organization statistics”.
Meetings that were moderated or withdrawned shouldn't be counted.

Additionnal context

Related meta proposal

Does this issue could impact on users private data?
No

Funded by
EU Commission