cubicweb #2953943 change the implementation of anonymous_session and anonymous_connection [validation pending]

The current implementation is a boolean flag set manually by client code after connection creation. This led to different way to decide a anonymous_connection should be True (eg. different in the test than in the actual application code).

This should not be client responsibility to set this flag. I suguest moving to it to a purely computed property. user in the "guests" group are anonymous, the other ain't

This ticket help the rework of the repository access API.

done in3.19.0
load left0.000
closed by#6cc13a0a9145 [dbapi] makes anonymous_connection a computed property
patch[server/session] Implement anonymous_session [applied][dbapi] makes anonymous_connection are computed property [applied]