Description

We currently (XWiki 15.10) don't have statistics of how XWiki is used in the wild. Right now we only have stats about the installs of XWiki and the installs of the extensions. It would be useful to have more information about how XWiki is used for knowing if a feature is used or not, discovering if some UI experiments help in discovering feature etc.

Now it's always dangerous to put such kind of usage statistics as it would give lots of information. The statistics would need to contain a UUID for identifying uniquely an instance to be able to properly analyze the data, making them a centralized point where we could know information about users and their wiki if we're not careful.

At the very least such mechanism should be opt-in only, with a question when installing / upgrading to ask users if they want to send anonymous data. We should probably provide a framework for allowing extensions to also send data, but IMO we need to be careful on the design, to not allow extensions to send too specific information: e.g. content of a doc should never be disclosed whatsoever, even a reference should not be sent.

Also we need to clarify where the data would be sent: XWiki SAS currently hosts an elasticsearch server for active installs data, the easiest would be to reuse it, but we probably need confirmation from the community that it's ok to put more data in that, knowing that XWiki SAS could access them.