Add config option for tenant field

[nsrosenqvist]

I'd like to use this for a simple multi-tenant application where these records would be separated by a team_id field. The field can easily be added by another migration, but I would like for a way to configure a field that should be used to store the tenant id. I imagine this could easily be done using the PanConfiguration class. I might submit a PR for this unless there are any strong objections to this?