Add /.well-known/nodeinfo endpoint

[6543]

add the nodeinfo endpoint (http://nodeinfo.diaspora.software/)

and add setting to metrics to specify if user statistics should be public or hidden.
if hidden just report the basic information (software, version, ...)

if public, report back total & active users

[6543]

would be used for e.g. https://codeberg.org/thefederationinfo/the-federation.info