Refactor session owner data model to just reference

[yinonov]

Is your feature request related to a problem? Please describe.
Changing owner user information might not get reflected in a session doc

Describe the solution you'd like
replace hardcoded owner object with a reference to a user document

Describe alternatives you've considered
Another solution could have been to trigger update of user owned session relevant data upon user doc update. but that fails with 3rd party sign in methods where user info can be edited elsewhere