Add a default role for row level security

[jjowsey1]

I want to be able to assign all users (including new ones) to a default role in RLS. Currently I have to assign each user to the role manually, and update the roles manually when users change. This limits the ability to use RLS with a larger user base.

[nishalit]

This role would be applied if none of the other roles were applied. This would have two advantages.

1. If an email address or security group was missing from a role, then the default (potentially more restrictive) role would be applied, rather than displaying all data. (Which strikes me as a big security flaw in the current implementation).

2. Would allow row level security to be applied using functions like UserPrincipalName() without having to name everyone with access to the report in a role.

[matthias_mann]

As it is now RLS is basically useless for managing larger numbers of report consumers. Manually adding every role is simply unreasonable and hard to manage in the long run.